I'm thinking the probe should be right at the hottest part of the tank which is probably not exactly in the middle but rather where you've stuck your UTH. Putting the probe suction cup on the glass above the UTH makes sense to me.
I'm not using a UTH. I'm using a moonlight bulb for heat and a paper towel substrate. I've got the dimmer on my bulb set so that I get about 79 - 82 F right under the bulb. the temp on the cool side is about 74 - 76 F. I've read some accounts suggesting to keep the warm side at about 90 F, a little too hot so the snake can go back and forth to regulate. I was keeping the hot side a little warmer at about 82 - 85 F but she was spending all her time on the cool side. Now that I've lowered the the hot side a couple degrees and put a plastic rock cave hide on the cool side and a coconut hide on the hot side she is going back and forth to regulate. I left her cardboard tube in there but she seems to like the new hides better.
I'm not using a UTH. I'm using a moonlight bulb for heat and a paper towel substrate. I've got the dimmer on my bulb set so that I get about 79 - 82 F right under the bulb. the temp on the cool side is about 74 - 76 F. I've read some accounts suggesting to keep the warm side at about 90 F, a little too hot so the snake can go back and forth to regulate. I was keeping the hot side a little warmer at about 82 - 85 F but she was spending all her time on the cool side. Now that I've lowered the the hot side a couple degrees and put a plastic rock cave hide on the cool side and a coconut hide on the hot side she is going back and forth to regulate. I left her cardboard tube in there but she seems to like the new hides better.