Jazz guitars are often played near the neck for that mellow tone.
Mostly this. Sometimes the top edge of the fingerboard is the rest.
With a sprinkling of "following the shape of the upper bout' and ' not obstructing the soundhole.'
I have seen instruments with play wear above the strings a la Basvarken, in the trad teardrop area, a la ilian's friend, as well as all sorts of places, but notice how those 2 specific examples are different. People play differently, and wear their tops differently. If you're playing somewhere between the twenty-somethingth fret and the butt edge of the fretboard as jazzers often do, those reverse pickguards actually are in the right place. To me a TBird guard has no other place to go and covers all the area that would be in danger with me playing it, aside from the raised middle part right above it/below the strings which is not feasible to protect in an aesthetically pleasing and unobstructive way.
There have been plenty of players (including our very own Uwe) who have claimed tonal improvement with unobstructed F Holes (in Uwe's case I believe he was referring to the acoustic/practise tone of an LP Sig or Cassidy). I have no knowledge about that tho.