Naw, it's no problem. The heater came with little "feet" (2) to be stuck under the tank on each corner. It raises the rear of the tank just a bit so air can get in there. I have it hooked up to a dimmer switch and inside the tank directly over the heater I have a probe that is connected to a digital thermometer so I always know exactly what the glass temp is.
The little feet I am talking about are simple spacers........you could use anything, tho. A couple checker pieces, bottle tops, name it. Just raise up the rear end of the tank or put a foot under each corner and raise the whole thing up 1/8 or 1/4" and you should be stylin'. As long as heat can escape and air can flow, things should be fine.