MTGuru wrote:
But I'll try throwing on a left strap to see if that makes any difference.

OK, I spent an hour or so this morning playing with the left strap.
I don't find it makes much difference, if any, to my left hand position, standing or sitting. So maybe the strap is not the critical factor. Tightening the bass strap a bit does help keep the treble side of the instrument vertical, which helps the left hand from assuming too weird an angle. Checking the mirror, my fingers are perpendicular to the bass rows, and the thumb up at about a 45 degree angle to hit the air.
Like you (I think), I'm not using the weak pinky (4) on the basses, just 3/2 or 2/1. I don't know if that's wrong or not. But I can still curl my fingers onto the basses without really changing hand position.
Your evil plot to force me to learn the basses continues to ruin my life. Curses!

_________________
Vivat diabolus in musica! MTGuru's (old)
GG Clips /
Blackbird ClipsJoel Barish: Is there any risk of brain damage?
Dr. Mierzwiak: Well, technically speaking, the procedure
is brain damage.