As far as the temps go, have you tried adding / removing substrate instead of changing the temps? Making it thinner to allow more heat to travel up words and running at a lower temp.
I usually worry more about what the surface temp of the tub is more than ambient temperature.
What is the ambient temperature of the room the rack is in?
96 also feels rather high for a temp at the tubs surface.

As far as the size of the tub itself, it is a large tub but with your hides and water they take up a lot of room. How big is the hide compared to the bp? Is he tight fitting in those hides? Even though there is not much open space he may not feel secure in the hide.

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