I think we may be overlooking something here. A "shooter" pointing his pistol at us is very likely NOT a guy aiming, isoceles or any other target oriented stance/hold. He IS very likely a guy committing a crime, pointing a gun in our general direction, NOT aiming or getting a sight picture at all.
My training suggests - make yourself small, in a different space, moving.
I suggest it's pretty darn hard to armchair pre-plan.
Sgt Lumpy - n0eq