As far as I can tell, it is crazy to shoot a single round per charge and make heads or tails about the result, so yes your only chance of making sense out of a ladder is to shoot it multiple times. But if you do this, then where is the savings in terms of ammo count? Barrel heat problems is the same in both, you just got to wait a let the barrel cool between each round.
As for same POA, well when I do OCW, I shoot 8 targets on a single sheet of 8”x11” paper, at 100 yards, that is hardly any change in POA, but if we are really worried about that, shooting 3 ladders would also require one to do the same i.e. change POA each time.