RAS,

One of the articles I linked to above seemed to show that test subjects immersed suddenly in cold water who did not have their heads covered, did in fact show a higher percentage of core temperature drop than those whose heads were covered.

The total heat loss over the bodies surface area didn't change, but the bodies reaction to the sudden cold probably caused the vasoconstriction that changed the core heat loss percentage (I could be misunderstanding the article, I'm not a scientist).

I'm not sure how this could be utilized in a survival situation unless you're willing to lug a Mustang suit around with you!