So it's not just a case of standing further away from a fire while wearing insulating clothing... alsd the fire itself is super-efficient at dissipating heat through the medium.

It does seema little crazy when you think in millions of miles, but distance in this sense is irrelevant, you have to see it as relative distances. Venus is approximately twice as far from the sun as Mercury is. So being five or ten meters from a fire is a resonable analogy.