Holding the magwell (sigh).
Holding further out the end of the rifle/carbine will give you more ability (leverage) on the gun, than holding in to the magwell does.
It both allows you to aim the gun at the target ("drive the gun" bothers me as a term for this, but you get the idea) faster, and control the muzzle much more effectively for follow up shots.
A lot of people who monopod the rifle for service rifle hold the mag well, which is fine for slow fire prone shooting. However the mistake is made that this translates to a good idea for rapid fire active shooting.
You POI shift on a non FF foreend in the standing will not be that much, as your pulling the gun back into you dont down to the dirt.