I will get a temp gauge for directly under the basking spot. It’s about 8-9 inches away from the soil. It’s a uva/uvb mercury vapor from zoo med. I’ve had him about a year and he’s grown an inchIts important to know the basking temp for two reasons:
1. If they can't get warm enough, it can hamper their immune system and ability to fight infection.
2. If its too hot, it can excessively dry out the carapace and contribute to pyramiding.
What type of UV bulb and at what mounting distance? This might be a factor due to the sanitizing effect of UV and overall well being of the tortoise.
How long have you had your tortoise. How much has it grown since you've had it?