Ok, i think i see what you mean a little better, especially as far as the air gap. Like an air gap between you and the S.B. That part makes sense, i thought you were saying you had to have a clear air space behind the S.B. to work.
Well there are ways to create some air gaps i suppose, rolling up some clothes into a tight roll placed over your body, but then you got to sleep like the dead, so not very practical i suppose.
Why does nature hate us so, why, whhhhyyyyy..???? Can't things be easy, light, effective, and cheap?
Why are we such wimpy creatures, with so little natural adaptation? Wolves don't have to hang around gear forums figuring out, "Gggrr arff arrff ruff ruff ruff Ah oooooh(translates) "Well Bob, let me tell you, i got these new down booties, and they are dah bomb, super light, super warm, and it only cost 3 rabbits. Can you believe it?"