That's where it can get a bit confusing. If you have two different pistons with a different number of holes, the one with more total hole area will have less pack. However lets say they have equal open area but a different amount of holes. The one with more holes will have more pack. I have a general rule, and it's really just personal preference. I use the same number of holes all around and only vary the hole size. If I'm running a 6 hole piston up front, you know I'm running a 6 hole in back too.