I'm wondering how your ambient temperatures vary so much from each side of the cage when you use only an uth (besides only the few hours of light use.). If these measurements are without the light then I can only assume such a high ambient temp could only come from the uth being WAY too hot. That would explain why he does not want to be on the hot side. Do you have a thermostat to control how hot the uth gets?

the substrate temp hot spot over her uth should generally read 88-92.

you said in the original post fake plants but in a separate post real plants. Do you have both fake and real plants in his tank? What substrate are you using?

ambient temps do not need to be as high as 85, as well 75 is the low end you would ever want. Drop the high end a good couple degrees and bring up the low end To 78. I like to keep my ambient temp at 82 through my entire cage, but inside his cool enclosure will measure 77-79 if he needs to cool down.

can you measure the temperature of the substrate using either a temp gun or a probe thermometer? What are the substrate temps on either side of the enclosure, as well as underneath each hide, and above the hottest point of the uth?

what are the size of his enclosures? Perhaps they are too big for him. They don't like large enclosures at all.

65% humidity may also be a little high to have at all times as well. During shed that is great but does not need to be that high continuously. Mid fifties is a great level to hold. Definitely don't need to do misting if it doesn't drop below 60%. Remember that if the substrate is wet, his enclosure over the uth will have much higher humidity than the readings outside of it because it will hold all that evaporated moisture inside much better than the tank itself will.

Also, even with all temperatures where I want them, one of mine does like to sit in her fake plants from time to time, although they are very dense and you can barely see into them.

i am pretty new here so I am learning, but from what I have learned thus far, these are the things I would check.