I sometimes notice that when I move to higher positions on the neck, my picking hand tends to move “by itself” closer to the bridge. Maybe it is some bad habit, or maybe I unconsciously try to keep relative picking position constant to preserve the timbre (which depends on where exactly you hit the string). I also noticed it when playing classical guitar with fingers. This right hand position change was more evident when I didn’t have dystonia in my right hand, now it is weaker but it’s still present (so it’s not related to dystonia). I’m just curious if anyone else here have noticed this effect.
I haven’t, but I’ll have to pay attention and check back in.
I’m going to hazard though that it’s not relatedly to keeping relative pocking position consistent - the position of the pick alone has a huge timbral effect on your tone, and the closer to the bridge you go, regardless of fretting hand position, the brighter and sharper your attack gets. My guess here is there’s something that you yourself like about hearing higher neck-pickup notes with a sharper, brighter attack, but lower notes you tend to like warmer and rounder and woolier - I’d be curious to see if this is related to fretting hand position or if it’s more driven by pitch. Or, if it’s some combination thereof - I could see maybe develping the habit to pick bass string notes closer to the bridge as you move up the neck, which do tend to get a bit wooly higher up the neck, but your change in picking location moves less on treble strings.
Interesting thread, either way. 
EDIT - just tried. I keep my hand closer to the neck while strumming, but move towards the bridge for single note runs, likely because there’s less deviation in the string as it vibrates there. As I ascend from the bass to the treble strings there is a slight bridgeward drift, but that probably is driven by an anchored forearm rotating rather than moving across the guitar and is a purely mechanical motion, as if I were to try to do this consciously for tonal reasons I’d probably move towards the neck on higher strings to make them fatter and rounder for single note lines.