I use tiles and i've never had a problem with heat. Only in the winter did i use lighting as the room temps dropped significantly, however after reinstalling the heater for the room, i was able to maintain a temp of 72-75 degrees.
The tiles do hold heat very well and yes the under tank heater is underneith the glass of the tank. I would not recommend putting it derectly under the tile then laying the tile on the bottom of the tank as the UTH requires a space to vent excess heat, thats why most or at least the ones i bought come with those little rubber spacers to put on the corners of the tank.
Are you using a Rheostat or thermostat with your under tank heater? Without them the heaters can become to hot, even with the tiles on top. Ambient heat can be increased by upping the room temps or using a simple low wattage light bulb on a timer to give day/night schedules. Because my gecko room is in the basement with little natural daylight this is what i plan on doing once i can get all of my tanks situated on one side of the room. I plan on installing one light above them and having it on a timer instead of leaving the room light on.
I hope that helps 
Red 
>>Anyone that uses a heating pad in conjunction with slate tiling for the leo's cage might be able to answer a few questions I have regarding this.
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>>If you put the heat pad under the cage, and there is a layer of slate above the glass, will any heat at all absorb through and heat the animals, or should the heat pad be placed against a wall instead?
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>>And, what about sticking a mat under the tiles instead of under the cage... would that make any difference?
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>>I have a 100 watt bulb on the hot side of the cage, but don't think there is enough ambient heat. Maybe, instead of a heat mat, should I get a ceramic heater?
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Crested Gecko Zeek:1.0, Ziggy and Zeus
LEOS: Boo: 1.0 normal , Bronx & Nala: 1.1 blizzard,
Lily: 0.1 patternless, Abby: 0.1 albino, Zoe: 0.1 reduced pattern, Dot: 0.1 hypo
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