Mine like it hot. Ambient never gets below 80 at any time, and I let it creep up into the low 90's during the course of the day. They also have a basking spot that is 95-100 degrees for 12-13- hours a day, but dark at night. Two CHE's on a thermostat maintain ambient for me.
Tortoise Forum
Tom
Dan
Your temps and set-up sound much like mine. I use a closed chamber so humidity stays between 80-90%. Substrate is dry at the surface but damp below. Torts don't touch wetness unless they seek it out. It has worked well so far, but I always like to compare notes with these guys.