Good replies, Everyone.
I am 6'1" and 175#s, not a linebacker by any means. I have always found that keeping my long, lanky arms as close to my body as possible to be more stable than the support arm towards the muzzle. That's why I use the mag well for support. Even when hunting with my BAR, I have always liked my support hand underneath the receiver, while that elbow can be supported on my hip, waist, etc. One of the Best Defense segments last year recommended a support hand as close to the muzzle as possible in case someone tried to grab the rifle, you had more control and leverage. While this is a very good point, the likelihood of someone grabbing my rifle while on the range or hunting is very slim. I don't shoot in many other situations. I find a pistol more than adequate for home defense, with a flashlight in the off hand, and don't use my AR for home defense.
Bucktracker - when you say using the grip as a point of reference, do you mean still gripping the fore end and not the grip?
Lastly, I enjoy shooting prone, and at one range we are required to shoot off of sand bags. The VG is difficult to remove for bench shooting, and can be a pain while prone. For soldiers carrying their weapon with a VG, wouldn't the length pose a problem if they have to go prone (which I assume they do) or while shooting over walls, through windows, etc?