First of all, I'm talking about when I'm outside, not in bed. I start covering my belly if there is strong wind, otherwise I start by covering my shoulders before covering the rest of the body, if the blanket is big enough
also the nasal passages since theres a ton of blood vessels. thats why it gets cold, because the nose is the first to restrict blood vessels in the head.
Cannot remember if the study was stupid or if peoples interpretations of it where. But when covered up else where you will lose a lot of heat through your head. More so then if just an arm or just a leg was exposed as with your arms and legs your body will slow down blood flow through them to try and converse your core temperature - it cannot do that with your head.
I have heard that you lose the most heat through your head from multiple sources as well. That would make sense, because I'm pretty sure the brain uses the most energy among all organs.
Edit: Probably depends on how you measure it. Per cm²? Total area? The latter makes it more likely that you lose most heat through your torso.
Bin mir aber nicht sicher und lasse mich gerne eines besseren belehren.
After reading through the comments, I'm imagining everyone walking around with a constant stream of steam puffing up from their head. What if the heat we lose was visible at all times?
Afaik there is a specific spot between the shoulders with brown fat that acts as a temperature regulator.
As a caveat, i read this in a (scientific) article decades ago.