I'm in the process of helping my gf set up a tub in hopes of acquiring a rainbow boa.

our tub has a couple inches of cypress mulch, a few holes drilled around for ventilation, and a UTH that is about 1/2 the floorspace for heating. Running the UTH uncontrolled(which is just for test purposes), it gets up to about 98 degrees for direct contact temperature. My problem is that it is not doing anything for ambient temps. It's freaking 66 degrees in the tub, but at least the warm spot is a decent ~80 on the top of the substrate.

Should I put a UTH on the side of the tub? What options are there for raising ambient temps within a tub?