is that *any* airflow between the window and the blind picks up that hot air and then recirculates it.

I have a cunning plan!

I am going to build "window baffles" at some point. 2 sheets of 1/8" plywood sandwiching bubble wrap. on both external sides of the plywood will be that spaceblanket material, and then wrapped around the whole thing will be fabric to make it purty

The space blankets will isolate out heat/cold, and the baffle will add a small insulating layer to keep the cold in/out, and heat in/out. These would be held in place via clips or perhaps pins?

Something to think about.

JJ