PnyKlr,
I think you're reading too much into what I said. =P
I used the tile because I don't like the permanence of the UTH being attached to that particular tank forever, or nearly forever. If I want to later use that tank for fish, all I have to do is take the tile with the UTH out from underneath and use it elsewhere. All the tile is for is to keep the UTH from burning your tabletop as ceramic is a very good insulator.
I've never used a rheostat/thermostat for my UTH's either, so I felt they were also too warm when attached directly to the glass and plugged straight in. Most of the newer ones don't seem to have that problem fortunately. But I had a couple of older ones that got hot enough to melt candle wax. A buffer of air was all that was needed to moderate the tempreture the low-tech way.
Raised or un-raised, either way you're "wasting" electricity. It's going to run the same amount regardless. Heat rises, plain and simple. The bulk of the warmth is going to be directed to the bottom of the tank. Excess warmth will escape around the sides. If the tank is laying flat on the table, essentially you'd have an all warm-bottomed tank, wouldn't you? Isn't the idea to create thermoregulation zones, a warm end and a cool end?
The main principle behind the feet is to keep the tank from pinching the cord and causing a short, and to secondarily moderate the temps underneath the tank. I'm sure with no air circulating under there, a crack from excessive heat build-up could happen. Its probably rare, but I'd rather replace a UTH than a tank.
I wouldn't use styrofoam as a "wedge" to keep the UTH against the glass. For me, that'd be a fire hazard waiting to happen. I'd say if duct tape isn't working, go out and buy a whole new UTH. They're not going to break the bank by any means.