I speak only from the medical point of view ( my basis for this being that I actually am a doctor…surprise!!!)…the gasket around your leg will not reduce blood flow to your foot unless it is extremely tight, and by that I mean “extremely”. You have 3 little arteries that take blood down to your foot, and they run with a fair degree of pressure in each. You can actually block off 2, and, in a healthy person, the other one will carry enough blood for your foot to survive.
On the other side of this coin is the fact that if your core (torso) temperature is low, then the body responds to this by constricting the arteries in the limbs so as to maintain “core” heat. When this happens, this initially means that people get cold white fingers and toes, and as the core temp drops progressively, the limb becomes colder. At whatever temperature it is (ie I don’t know), this protective mechanism prevents blood flow to the degree that the blood flow to the periphery is insufficient for the digit to survive, and that is where frostbite cuts in.
Additionally, if you are wet, the evaporation off the skin drops the skin temperature further , and adds to the whole exercise.
SO…to have warm feet, the bottom line is to ensure that your core (torso) temperature is normal (most heat is actually lost through the head, leading to the well respected adage of “wear a hat if your feet are cold”), meaning that you should also concentrate on keeping your torso temperature higher, and try to ensure that your skin stays dry. Therefore better to wear some head-covering at night, a duvet, and some quick drying thermal socks, than to sit around wearing neoprene socks , through which moisture doesn’t evaporate.
There is a complicating issue here with vapour barrier clothing, which works by preventing vapour (and therefore heat) loss, although these only work in particular temperature ranges, where you aim to prevent yourself sweating. I live in Australia, and it just isn’t cold enough for vapour barriers to work here most of the time, so I should digress to one of our US experts about this.
Hoping that some body physiology is useful…