Female armor rule in fiction, how do I love thee...

Less armor on females so they are more "mobile" and easier to dodge, but sacrifices defense. While males tend to bulk up the armor for more defense yet mobility and speed are negated.

Males tend to be stronger than females, so wearing bulks of armour wont be much of an issue. Females tend to be more flexible, so less armour will give them more freedom to move and use that flexibility.

None of which explains why gigantic shoulder pads are apparently an acceptable tradeoff for lack of protection for internal organs. But hey, midriff.