Tipi coda: musing on history

Tipis, as I learned, are surprisingly sophisticated:
there's a lot more to them than just a bunch of sticks and canvas.
However,
one thing seems to be missing:

There's no door flap.
I forgot to ask about it, but they MUST have had one,
for privacy,
for warmth (especially in winter).
I did learn that the winter tipi peg-down would have been different, too,
closer to the ground,
and presumably with some kind of insulation along the groundline.