I should know this but I'm not positive. Your (and your enemies) DT is an overall rating based on what pieces of armor you're wearing isn't it? In other words, though visually the armor isn't protecting your head and limbs they still have the DT the armor provides overall, correct?

Armor cover all, if you have a suit with DT of 10, or a head cover with a DT of 10, you still have a DT of 10.