In my head, I see it the same as guys and girls that use hammocks. They sell and people use under quilts for a reason.
Airflow beneath you would allow heat to escape. Be drawn away from the body, like the ground does. Although not as bad as the ground, I am guessing.
The hammock example would be more extreme, as they'd experience far more air movement due to wind than you would inside a tent or tipi.
I think the way to look at it would be sleeping on a pad without anything on top of your body. You are essentially insulating one part of your body while exposing one-half of your body with no insulation to the ambient air temperature inside your shelter.
See? I guess I already knew the answer when I asked the question in my earlier post. I was just hoping there was some type of unicorn that made the cot magical!