The black poke-through on heads is because the hair is larger than the head, so tell me how does increasing the hair size fix that?
Really, increasing or decreasing parts of the hair or parts of the head all work. The problem stems from a collision of two surfaces (even though one is transparent, that apparently isn't checked for until too late in the calculations and the problem rears its head). The solution of scaling is to create separation between the two surfaces (the head and the hair's scullcap). Which object ends up on the outside and which on the inside when finished doesn't really matter. Although depending on the exact hair asset's fit, which type of scaling will solve the problem with the least amount of change will vary.
(but I will add that the hair asset being parented to the body means it can often pick up any scaling done to the body as well... meaning separation isn't actually created... whereas scaling the hair never also scales the head)
