Your snake is probably too hot. They don't really need you to try to guess whether they are too hot or too cold, they will move around themselves to regulate their temperatures. If you don't use a digital thermometer to read the temperatures or have some kind of temperature control device (rheostat or thermostat) to control the temperature, it would be a good idea to invest in them. Do you use a UTH on the warm side of the tank?
In regards to the issue of not being able to raise the temperature, I don't know what to tell you. I keep my BP in a 30 gallon glass tank. I did the foil treatment and I use a CHE to raise the temperature on his cool side. The foil treatment works great for me. Maybe try covering up a little more of the roof? That's about all I can think of. I'm sure someone more experienced will chime in and try to help.
Also, I'm not sure if this is possible, but maybe your BP prefers the texture of his other hide.