Higher /p settings don't influence the %MF calculation, but increase the amout of drops for regular monsters, act bosses and a few super-uniques, e.g. Nihlathak. Monsters like Pindleskin don't drop more on higher /p settings, just like random bosses.
Higher /p settings in certain MF areas can still be useful for some time because they provide more exp.
Higher /p settings in certain MF areas can still be useful for some time because they provide more exp.