thanks for the info.
If it were me, I would provide a hotter hot spot (100-110 F) on one end of the cage, preferably a ground or under cage heater. Hot rocks don't provide as much of a gradient as do under cage heat elemants. Keep the cool end option that you have.
I would use some sort of bedding (I use aspen) so it can tunnel up to the heat source as near as it wants to. KEY is that they like to stay hidden (even when thermoregulating) and are usually underground or in tight crevices. Bedding allows super concealed options both security-wise and temp gradient wise.
Alterna use butter dishes and hide boxes too. However, if you provide tighter, darker more secure options that allow them temperature choices, they usually use those more.
If your snake is sick, look for it too spend time down on or close to the hot spot. You may have to go with a second round of antibiotics if this doesn't work.
Good luck.