Seems like enemies can only hit to the body. I’ve found that after all long tough fight all my body armor is almost ruined, but the helmet is practically undamaged.
I fought against whole Ratae garrison withot a helmet at all, and while i recieved a dozens of hits to the body, that broke my plate and hauberk totally - there where no critical hit or something to the head at all.
The same situation with the leg armor - I wear it more in aesthetic reasons )