I can say good point.
It seems to me that to be effective at self defense, one would have to go on the offense mentally, even if just for a few seconds. But that is not who we are (most of us).
To answer the question, I can see shooting the perp until he is down off his feet and no longer a threat...but shoot him in the head again as you step over his body? Eh, that sounds a little bit too far Tom Cruisish...Prolly get in trouble too. Stayin put sounded like a good idea after the first round of shots.