Why do we call them that way? It's not that they really resemble a (human) heel...

Anyway, that was just a distraction that caught me when thinking of a title for this post.

I don't think I have to tell anyone here what the common archtop heel looks like: something rounded that doesn't protrude too far from the rims and doesn't have too much "shape shifting" going on. My Loar has one like that, of course, but also my Cabaret. My Gretsch Alligator however has what they call a "moderate vintage V" profile with the kind of heel you'd expect *). It's what I learned to play on but as many I did have some problems getting past the 12th fret. Until my teacher kicked in the open door that I could move my thumb towards the treble side
Earlier today I was doing my usual warm-up LH runs (on the Cabaret) and once again my hand did something while coming back down from being over the top that misaligned my pinky. This time I had a look to confirm that there was indeed no gradual asymmetry designed to help guide the thumb and hand into (and supposedly out of) the appropriate position for playing beyond the neck join.
Classical guitars don't have that either AFAIK, but they have Spanish heels that probably force the thumb to move towards the treble side.

Where does the heel shape used on archtops come from, and is there an ergonomic aspect to its design? Is there a rule of thumb (pun intended!) to keep in mind for getting into and out of the highest positions?


*) interestingly the normal/"official" heel on baroque and earlier violins is very similar - minus the V aspect.