Greg - The friend/foe recognition adds a completely new dimension doesn't it!
That little drill we do at the range really is an eye opener for most gung-ho concealed carry people. If you set the stage you can create a little hype, add a little distraction, and not knowing when the target is going to start advancing and you realize 21' ain't nothing.
Taking a sight picture.....ain't happening.
Coat zipped or buttoned........ain't happening.
Fumbling the draw..........knifed.
You must put a lot of thought into where the gun is placed, what it's placed in, and what you conceal it with.
Practice the moves over and over and over. Clear, grip, draw, and get the muzzle on target asap. I try to have the muzzle rotating up onto the target as soon as it clears the holster/wasteband. My free hand joins the grip during that rotation, and first rounds are discharged without advancing the gun towards the threat. Pretty much like a gunfighter in a quick-draw fight.
Live fire practice and more practice until you can comfortably look the rounds into the center of mass from the hip or sternum height firing position at 15' with a stationary torso target. Once that's comfortable, start practicing on advancing targets. Teach yourself you do not need sights to place accurate shots.
It's a lot of fun and real challenging.