Don, I'm starting to suspect I'm like you with the eye issue. When I first look at a spot or anything like that trying to determine left or right, I can see two, kinda split in half and both fuzzy.
Dave, the M9 was used with the sights, I didn't use the usual triangle stance (which is basically legs about shoulder width apart, body parallel to the target), we were taught and used the Weaver stance which is more inline, perpendicular to the target. You have to align your eye behind the gun. I started thinking back the almost fourteen years now, and realize I was closing my left eye then, just never slowed down to notice it.
I can shoot any which way I want to, instictive, gap, or split vision only with the one eye squinted or closed. I don't see the arguement of the range estimation being off, that's done either before drawing or while drawing before I close the eye.
Alot of good info has been shared on this thread, hope it helps someone else out, or for someone to try something new, never know till you try.