[Imp]

Don't do tests Chuck just observe & overtime you sort of pick up stuff.
Not counting hitting a soft spot or warhead size AP at very short ranges seems to have possibility for overkill so Pen of 6 might give 7 or 8. Sometimes hits with slightly less Pen to but not as common.
HEAT has a much bigger range consider the listed Pen as more like an average it has more chance to deviate both up & down & does so by a greater amount.
Feel free to test but HEAT produces more unexpected kills & if anything I am watching the info box to decide what concealed weapon is firing at me or for asterisks.