If the area has same glass coating as that in the roof, it seems to keep radiant heat out as well as (on our Model 3) the solid areas of roof. We do however have a small area of rear glass that appears not to be coated and, along with windscreen and side panes, that is where the heat radiates into the car. Our sun shade radiates (within a degree or so) the same amount of heat as solid areas of roof which is significantly less than the windscreen and side windows. The glass roof does a remarkable job at preventing heat transfer although does itself get very hot which is a different problem to solve.