I have a 36" wide tank and need to regulate the temp for my crabs. Heating my whole house to 75 degrees in the dead of winter to keep my crabs even at 72 degrees (it's an old house with poor heat containment) isn't probably very economical or environmentally friendly.

1) Do I need to send the heater back and order a shorter version that heats less of the cage?
2) Instead, should I wrap the heater around the corner so that it effectively heats less of my crabitat? This will be ugly if I try to cover up the heater and could overheat the tank silicone possibly?
I want to do the best by them. Is having the Ultratherm along the full length of the back of the tank bad for the crabs?
P.S. If my 35" is a problem, I'm going to contact The Bean Farm and others that sell the Ultratherm and recommend that they provide this instruction in the product description so that others don't run into this problem. Frustrating to discover this after getting it, and I did quite a bit of research before ordering.
Thank you,
Steve