Why is there a difference in AP when I buy pieces separately instead of a whole armour? For example, a flak helmet has AP 2 but if I get Guard Flak Armour it suddenly has AP 4. Is a helmet thinner when I don't wear it with the rest of the armour? Or is the normal flak helmet for "civilian use"? The same thing applies for mesh and carapace armour - the separate pieces have a lower AP.
It would be nice to be able to buy armour piece for piece, so I could customize it.