Now we’re talking 
Ha, you cracked it thank you! I think my whole technique is indeed built around that configuration.
I guess this means - if I want to keep doing the same thing - that my currently optimal solution [local optimum of course - not global 
] is to alternate between standing and the performaxe position.
Most likely personal. I think it’s just all the years I played (or I guess I should say attempted to play) ‘true’ classical on a classical guitar, everything just feels right to me in that position. Open position chords, even chromatic scales on the low frets. For what it’s worth, it doesn’t matter though - I still can’t play most of the stuff you can lol! What you’re doing is clearly working!
Left hand: your fretting hand (edit: I said picking hand, I mean fretting … ) elbow should be closer to a right angle. That fretting hand is giving me pains looking at it, you’re in a classical position but with electric, it’s not necessary. Straighten the wrist, means try to get your thumb higher up on the back of the neck, def never below the half line.
[edit: reasoning… clasical guitar fretboard = wide chopping board, electric no so much.
Also, the straight wrist helps with vibrato (twisting action) & bending (push/pull action) though in reality it’s a mix of both, but twist more than push/pull for most things, fulcrum is the thumb duh ]
Right hand: It’s in a right angle; should be 135 degrees approx.
[edit: reasoning… uses more body chi, improves angle of attack for me. I actually realized this going from the Strat to the LP, diff bodies, realised the whole guitar position revolves around my picking hand angle of attack on the strings, the rest will follow.]
All this means your headstock is too high and put your guitar slightly to your right against your right leg. It’s ok if it tilts a bit forward from the bottom.
[edit: if necessary tuck your right leg under the chair to get the right vibe, then you can adjust your seating apparatus accordingly.]
Bring your arse upfront a bit and sit back more. use a small cushion for your lower back if needed.
[edit: sit back means, keep your shoulders back, arse in front so your body is tilting back, it’s also a counter balance for the guitar.]
These are my recommendations, hope they help.
I think it’s more likely that he’s trying to maintain a preferred right arm position. Pulling the headstock closer (dot product with chest normal vector = 0) would require him to thrust his right elbow forward by rotating his arm at the shoulder, which would then require modifications to some combination of his right elbow angle, wrist angle, and/or picking mechanic, which I’m guessing he wants to avoid. Twisting his torso moves his right shoulder forward so that his upper arm can drop down to a more neutral and comfortable position.
At least that’s why I do it.
One of the big differences between acoustic and electric posture comes from the thickness of the guitar body, which seems to require more of the right elbow thrust in any sitting position. To someone who is more habituated to a thinner bodied electric, maybe that thrust feels like unnecessary tension that should be eliminated in the search for easy.
I also find that there are fretting-hand benefits to the forward-thrusted headstock. Specifically, access to upper frets requires less radial wrist deviation. The effect on the fretting wrist of pushing the headstock forward is very similar to the effect of elevating the headstock in that regard.
Again, just my personal experience. Maybe this applies to Tommo, maybe not.
Like this: https://www.youtube.com/watch?v=YYc9o9ROOZ8
You don’t even have to hold the guitar in that position - it locks into your legs.
That’s what I see too. @tommo, I also notice that there’s a pretty big gap between your elbow and your torso. I think conventional wisdom for “classical” posture (someone correct me if I’m wrong), is for the elbow to stay closer to the torso, with reach toward the nut achieved by external/lateral rotation of the shoulder (versus abduction of the shoulder).
I mean, what you’ve been doing has produced great results, so I take it you’re only investigating this academically, or to better understand the hows and whys of what works for other people.
Edit: I don’t think anybody does “strict” shoulder abduction when they fret toward the nut, it will always be some blend of external rotation and abduction, so it’s more a matter of proportions. And I may have underestimated how much external rotation you’re doing (your “seated, classical” photo has a major shouder external rotation component, though you still seem to have quite a lot of abduction going on with the fretting shoulder too).
Further to what @kgk said, I think the many hours you put in seated with the guitar on your right leg habituated you to a fretting arm setup that was optimized for that guitar position and orientation (guitar offset to the right, neck pointed out from your chest to a significant degree).
I mostly practice standing. When I sit, I sit with guitar on the left leg and reach toward the nut via external shoulder rotation. I thought of myself as facing forward, but motivated by this thread, I examined more carefully and found I do rotate my torso slightly to the left. In my case, that torso rotation doesn’t result in any discomfort. When I try putting the guitar on my right leg, I find that reaching toward the nut via shoulder abduction becomes more comfortable than reaching via shoulder external rotation.
I also suspect that reaching toward the nut via shoulder external rotation help keep the elbow further “forward” than reaching toward the nut via shoulder abduction. This may help with keeping the wrist straight, and some casual google image searching of famous classical players seems to show a tendency for the forearm to approach the neck “from below” rather than “from behind”, at least relative to most rock players. It seems to me that approaching “from below” would make it easier to keep the wrist “straight” relative to the forearm, especially when fretting the lower pitch strings.
Final thought: reaching toward the nut via shoulder external rotation will mean that the angle of the hand will be different when fretting closer to the nut than closer to the 24th fret, while reaching via shoulder abduction should result in a more consistent hand angle. Open to opinions on whether one is better than the other, or if it really matters.
A-ha- so I’m not crazy after all. I’ll explain…
I was actually toying with the idea of flipping a lefty Squier upside down and cutting a scoop into what would now be the lower treble bout from righty persepctive, so it would cup the thigh. The idea being to solve the problem that I think a lot of us have while sitting: the right shoulder hikes up too high (in an effort to position the picking hand correctly). It would be my practice (while-sitting) guitar.
That seems to be what the Warlock accomplishes (aside from looking righteously metallic;) Check out the guy’s right shoulder - ahh, the comfort.
I was going to say one thing about guitar body shapes: If one wants to comfortably play with the headstock far from one’s left shoulder, one can take a Flying V and put it over one’s right leg, like the enclosed image. (Indeed, the first time I noticed this was Wolf Hoffman, and I copied him, but now I see lots of people doing it.) I think that @tommo should try this, as it would be comfortable and natural, and fit his ergonomic preferences. Oh, and look cool, of course (win/win).
I also see @induction’s point that this might really be driven by the right arm… I wouldn’t be surprised.
CtC is an amazing place, I would never have even contemplated any of these issues before, but now they are so important that I’m embarrassed to have overlooked them in the past! 
You are very wise, and that’s how I sit with a Flying V (but at the edge of a chair). I think that Fender had a body that almost wanted that, let me see if I can find it…
How do you guys using the classical position get around the issue with twisting the torso to the left and pain in the right shoulder blade from extending the arm round to pick?
So cool. I’m only guessing, but I’d bet that right-shoulder-hike had something to do with this innovation.
As for twisting torso… If you’re not ready to hack up your guitar body, you might try something that’s worked well for me. I put something about 8-10" high on the floor and put my right shin down on it while sitting. This lowers my thigh, allows me to position the guitar without hiking my shoulder - and without forcing my torso to twist.
This is interesting, it shows how John Petrucci sits, where he might (?) have a slight rotation in his spine to keep his left shoulder away from the guitar? I also looked up Michael Romeo. I think that both of these guys are close to what I view as the most ergonomic way of sitting, but be warned that I know nothing about ergonomics!
Petrucci twists his torso in the video a lot, this would kill my spine and right shoulder after a short time and Romeo is pretty darned hunched over.
The more I think about this the more I think the classical position is not suited to sitting down electric guitar and that it’s better to use the rock position and just try to sit up straight.
The hunching/twisting/right shoulder/left wrist issues are reduced quite a bit (for me at least) by pushing the headstock forward in classical (i.e. left leg) position.
That said, I constantly move back and forth between the rock (i.e. right leg) and classical positions when I sit. I doubt I spend more than 10 minutes at a time in one position before switching.
And I push the headstock forward in rock position too.
I have no problems when I use a classical-ish seated position, even though I rotate my spine slightly when I do it. But if we’re bottom lining it, I think standing with a strap that you’ve adjusted optimally for yourself is superior to any seated position. Sitting is highly conducive to slouching no matter how you slice it. Standing with the guitar on a strap is ideal unless you sabotage yourself by choosing an excessively massive guitar.
Classical position all the way. Keep your back as straight as possible, relax your shoulders.
On the right leg kills my back because of the hunch. I use the left leg (with small footrest), but the headstoke pointing forward a little and my right leg is point out to the right (about 1 or 2 o’clock)
I found this video on youtube, to me it’s the best you’re going to get I think: https://www.youtube.com/watch?v=qtZ7EUrsnR8&list=RDqtZ7EUrsnR8&start_radio=1&t=243
Classical position feels great for picking but the lower back and shoulder blade pain really isn’t worth it. I think there is an element of that I have played for 20 years in the rock position so my body is used to that whereas the classical position guys have gotten their bodies used it over the years.
