Mike, thanks for an excellent article. Though I'm sure there would be enormous variation, it would be interesting to learn what the relative percentages of water vapor emitted by the breath and by the skin are during sleep. Suspect that breathing supplies much of the water vapor, and wonder if it wouldn't be possible to have some kind of heat-exchanger which would allow one to breath in an otherwise closed bivy sack directly to the outer air. I use a MLD eVent bivy, and often have it quite closed up to help with heat. (Just zipping up the mosquito netting, with the main fabric of the bivy unzipped near the breathing area, can add a lot of warmth).
The info, and explanation, about choosing a site with a minimal view of clear sky is invaluable. Have noticed this phenomenon when comparing warmth in a grove vs in an open field, but always thought it had something to do with the stiller air in the grove and the warmth emitted by trees (which it may, somewhat, but I'm sure the sky view is more important).