I carry a Glock and try to practice 2x C of Mass, then one to the head at various distances.
What distances? Unless the BG has a gun or throwing knife, you'd be hard-pressed to defend a shooting at much over 30 feet. It should take about 1.5-2 seconds to draw, properly aim, and fire the first round. A human can run (at top speed) about 30 feet in two seconds. If you have that much warning, you're lucky. Most SD shootings happen at less than 10 feet.
Others advocate 3x C of Mass and reassess, etc
I was taught two COM and reassess the threat. Head shots are EXTREMELY difficult under stress at a moving target. You MUST think of your background/bystanders when in public. You won't see LEOs going for head shots. A head shot might line you up for a murder charge, too, even if in a SD situation. You don't shoot to kill, you shoot to negate the threat.
With my LCP mousegun I cannot do head shots rapidly(point shooting) unless really close so I practice 4x C of Mass and reassess.
The mousegun is obviously a poor second to the Glock.
No, it isn't. Mouseguns were NEVER designed to compete with or replace larger, more accurate pistols and revolvers. A mousegun is a belly-to-belly, up close and personal, "get off me", SURPRISE gun. It's designed to be a last-ditch, "rut-roh, the BG caught me napping" SD weapon. If you're accurate with one at 5 yards, you're doing great.
Any suggestions on round placement/management for either gun??
Practice accuracy first. Take it slowly. Speed is nothing if you miss. Use the sights. "Point and shoot" either from low ready or looking over the top of the frame takes a LOT of practice with the same gun. Switching guns changes everything.