Its not going to matter in a real situation. Self defense shooting is not like golf, where you get all the time in the world to adjust your grip, your foot position and wiggle your butt before you swing.
You will running, falling, dodging, sitting or whatever during a real shooting incident. Learning a proper shooting stance is fine and needed to learn; however, once one has progressed into combat shooting, it is foolish to think that proper stance is going to be achieved prior to firing.
But, I do think that the whole proper stance thing is a carryover from military and police style training. Stance does have a lot of merit in some situations. It does stabilize the shooter, and it does make it easier to deliver accurate shots. That tends to be a little different situation than a self defense shooting.