A uth should have a very thin level of substrate over it. Less than 1/2 inch, I have about a 1/4 inch. A four inch substrate will not allow any heat from the uth to reach the surface.

I'm not familiar with the tropical setup you had or what it comes with it. I would unplug the uth and use a heat lamp to get a proper hot spot.

Not being able to see your setup I'm blinding going to suggest having secures hides and alot of cover for the snake to move through. If the new cage is a good bit larger than the old it may not be feeling very secure and adding tight fitting hides (atleast 2) and cover (more plants, driftwood, fake plants, etc) can really help reduce stress in your snake.