I am - painfully - trying to understand this thread ...
and starting to wonder ...

"Did I miss something or what ?... Am I supposed to hike buck (sp?) naked (like that guy, doing exactly that in Great Britain... when he is not serving time in jail for exhibition !!! ), with only a hat on my head ?????"
(see my avatar ?!!)

I guess, then I would loose much more heat from other body parts ..

My own take (not a scientific one, I fear ..) on that "heat loss from head" stuff was (up to now...) that if you are normally dressed and wear NO HAT, then a great deal of heat is lost from the head area.
Covering your head might help keeping warm, more than adding a layer elsewhere.
OTOH, in the dead of winter, adding a parka over a simple T-shirt might beat the hat thing as far as rate of heat loss is concerned....

___________________________

Edited :

Oooopsss... I had not read all the recent posts.
Looks like Raydarkhorse, or JCWohlschlag also said about the same thing, if differently ...