The method of crosspicking your using here looks like it’s very similar mechanically to the first “picking mode” I discussed in my picking styles thread.
When I first developed this picking mode as a teenager, I definitely noticed that string tracking was the primary problem as I increased the speed, and that missing strings was the most common type of failure.
I focused on several key issues which helped me.
As in all cross-picking movements, less pick depth allows for a larger radius to the arc of the picking movement. I knew this academically, I had a diagram and calculation written in a notebook similar to the “golf club and flamingoes” calculation in the Steve Morse feature (which can be solved using just the Pythagorean Theorem!). I think I had a tendency to try to flatten the movement arc by picking with less and less pick depth until I would eventually start whiffing completely. I had train myself to maintain a constant pick depth that was a compromise between shallowness and sureness.
I also noticed that a small part of the problem was that I had a slight tendency to change the height of the fulcrum for this pendulum-type movement very slightly as I moved across strings. Ideally, the height of the fulcrum would the same for each string you play on, so that as you would move across strings the position of the fulcrum would define an arc matching the radius of the fretboard.
I had this aspect of string tracking slightly skewed, with the neutral position being set by the G and D strings (the highest strings), and the arc of the changing fulcrum point being flatter than the fretboard radius I was using at the time, so I most frequently missed the two E strings.
I corrected this mostly by ensuring that I wasn’t using any wrist movements for string tracking, with the elbow being mostly responsible for tracking.
I first achieved this on a Strat with a 9.5" fretboard radius, and now most of my guitars have 16" or 20" radii. I know you play vintage Fenders with 7.25" fretboard radii, so tracking fretboard curvature might be a more significant problem for you.
Finally, I noticed that when practicing one note per string patterns slowly, I tended to make distinct switches in fulcrum position with my elbow, but when playing faster, the speed required that the tracking movements become smooth, so my elbow was constantly moving, as in a sweep.
After noticing this, I tried to make the tracking movements more gradual when practicing, and I feel that this helped me.
How do you feel this method of cross-picking compares to the method you utilised in the Steve Morse Interview analysis, which (if I remember correctly) had a pad-to-pad pick grip that more closely resembled Steve’s method?