under tank heater

[cordell]

I just bought a Zoo Med under tank heater for my BP. My tank is 55 gallon and the heater says it will heat up to 60 gallon, its the big heater. Anyway where do I put it, under the tank or side mount? And where exactly, middle or one end or the other? Substrate is 2 inches of cypress mulch and top soil, about a inch of both with the cypress on top of the soil.

Thanks