Other very subjective tests -
Singlepane versus thermalpane windows:
There is a very noticeable difference up to say 3 or 4 feet.
I "Feel the Cold" - I sense that radiant loss easily.
Lack of ceiling insultaion:
I bought a house with no insulation in the attic. (don't ask.)
While sitting at the dinning room table I could feel a dramatic difference when my legs came out from under the table. The sense of a cold ceiling was real. It went away with 18" if fiberglass.
There may be a difference between sensing incoming radiation, say from the fire place, and sensing a Loss of heat, say to a window pane. The quantative number are certainly very difference.
Al, your formula indicated "Radiant loss is small compared to convection", but in terms of sensible comfort, I believe controlling radiant loss makes a difference.
And to muddy the waters a bit, I also believe that much of the "space blankets are warm" sensation result from their vapor barrier effect.
Now - to sort out all of the science....