I don't usual worry about which is on front or back if it holds the top of the bag together. If the snap is on a flap I tend to put the male side on the flap and the female side on the bag.
FYI- I cut a round of plastic from milk jug or top of oatmeal box to put over the prongs with the metal disc that comes with the snaps. I make it a little bigger than the metal disc and think it gives more support (and it's washable).
Pat