Shooting at distances is good to know, but not the most likely scenario. With experienced criminals they will be on top of you before they make a real definitive move. These are people who use violence as the first option, just as natural as you breath. You may not get any of the cues you might expect. Just because he is in what you call your personal space is not justification, and that does depend on the situation. You have to consider an outsider looking at the situation and deciding if you had reasonable belief.
One of my most practiced drills is the contact drill. Warding off the attack as you draw the handgun from concealment with one hand. Rolling that handgun at waist level and delivering shots to the opponents pelvic area. Forget about COM in this situation, but rounds in him someplace, anyplace. Then make your distance.
Understand that with an experienced thug things happen suddenly and very quickly. Several that have assaulted or attempted to assault me came out of nowhere, from completely calm to murderous instantly.
28 years in corrections walking the locks, been there, done that.