Well.. I can see your points, but it seems to me you're analysing the electric guitar fully clean.
Once distortions are applied, the rate of fall-off of the harmonics changes quite dramatically, as distortion will add quite a lot of additional higher harmonics.
Hence my suggestions on using comb filtering in the upper mids to [guitar] treble region.
BTW, I'm well aware of the comb filter in the ucab, just never calculated it's frequency range.
Now, it is entirely possible that I'm in error on this, and if so, very simply because I might confuse my above statements with the fact that neither the ucab nor the MP-2 rolls off at the high end are any more than a 1st order function - like you stated.
As such, it's absolutely possible that I mostly just need a steeper slope on the high roll-off, check the results, and only then look into what else might be needed.
Another mechanism lending to your observations is that, when playing high up on the board, distorted trebles does sound less fizzy, which, even when the roll-off is a mere 1st order function, nevertheless does make the harmonics hit the slope much earlier than when playing further down.
As such, those higher notes automatically gets filtered off decently more smoothly, again supporting your comments.
Hmnn.. I'll go do the Om thing, poke the akashic in the 10th dimension, and ask my spiritual masters for guidance..