Be very careful of sunlight it can amp up the temps in a glass tank (greenhouse) very very quickly. I would not take away the primary heat source. You cannot thermo regulate for your snake. If you can add a small air space to the uth. Or try a adding a sheet of glass (sanded edge) just over the uth under the substrate to absorb some of the heat.

The question I have is what are the ambient AIR temps in the enclosure? Ambient temps are often ignored in favour of surface temps of hot and cool sides. But ambient air temps are just as important, the long lung runs beside the heart liver and most of the large arteries and veins in the snake hot air in the lung(s) will warm the blood and the core temp with it. The snake can lay on a cool surface for ages but if the air temp is hot the animal cannot cool off.