Hi,
Double check it by putting the probe under the substrate inside the hot end hide - the hides can trap heat if your using a UTH.
Also don't get tied to the idea he is only in the waterbowl because of overheating - they can also do it because they are coming up to a shed and want higher humidity or because they think it feels more secure than their hides ( water touching them on all sides kind of thing ).
Are both hides identical?
Just in case he simply doesn't like the hot end hide.
dr del