How come sometimes I only want the blanket/covers over my feet and not legs?

The monster under the bed can’t get you if :

You’re feet are covered.

You’re head is covered.

I thought this was common knowledge.

You are feet are covered

You are head is covered
- There’s a lesson somewhere in their.
And the fact is that wearing socks don't help. Only blanket is effective against those monsters.
Honestly, this is kinda like the perfect answer for me. I love this kinda shit, Monsters under the bed lol
This response would be even funnier if you like totally doubled-down and prefaced it with "Everybody knows that..." + Your current prose.

;)

Conversely, I like to have my feet poke out from under my duvet.

Same, my feet are always warm or hot, I walk around all winter on hardwood floors with no socks.
- I rarely wear shoes when not outside and will be bare foot as much as possible (so I have Hobbit feet). I do have Raynaud's though, so have made to wrap up a bit warmer these days.

"Vasodilation occurs in superficial blood vessels of warm-blooded animals when their ambient environment is hot; this process diverts the flow of heated blood to the skin of the animal, where heat can be more easily released to the environment. The opposite physiological process is vasoconstriction. These processes are naturally modulated by local paracrine agents from endothelial cells (e.g., nitric oxide, bradykinin, potassium ions, and adenosine), and by the autonomic nervous system and the adrenal glands, both of which secrete catecholamines, such as norepinephrine and epinephrine, respectively.[6][7]"

It's the opposite of vasoconstriction, which occurs when you're cold and your extremities have less blood flow to prioritize the warmth of your core organs.

I learned about vasodilation in the medical tent at a music festival, finding out that high grade cannabis causes it in some people. 10 minutes after I hit a pipe, I passed out….. and stayed out
- I guess you could probably help me out then, I could take the unfinished bowl off your hands. Lmk

For the same reason that orgasms are better if you're wearing socks.

This is the first I'm hearing on the matter/association between socks and orgasms 🧦🍆💦
- I read it in some medical journal many years ago, but I already knew it from experience.

Because blood pressure, your feet are most far and during the night you don't use them, less blood mean less activity and so cold.

Sounds like circulation issues, exercise, Diet, and blood pressure will have a impact on how well your extremeties get blood and feel "cold"

Feet don't have a lot of fat for insulation so they tend to rely on the circulation system to keep warm. Just like your hands.

Cold feet/hot legs