The hair should have associated morphs that can be adjusted to prevent the cap from overlaying the forehead. These are usually found by selecting the hair, going to Parameters and then Actor. usually they will be under Morphs or something like that. Probably lowering the head size should resolve it.
probably_dave's approach is one way of doing it. Another would be to modify the opacity on the hair cap surface so that it's transparent. (Although that will sometimes allow scalp to show through the hair. The reason PA's color their hair caps is so that they don't have to make the hair so thick.)