Your UTH should cover 1/3 of the bottom of your tank, no more than 1/2. The UTH should produce the level of heat you need. The top of the substrate on the warm side should be kept between 88-93 degrees. You need a digital thermometer with a probe to monitor the temps on the warm side. More than likely you will need a thermomstat or rheostat to control the temperature as UTH can get well over 100 degrees. So you probably wouldn't need to use lighting as an additional heat source, if your UTH is the right size.
As for the astroturf, I would say it's not a good idea if you are talking about the stuff I'm thinking of. It is very rough and Leos have sensitive belly skin. Instead you can use Repti-carpet, slate tile, non-adhesive shelf liner, paper towels or newspaper, all are very safe.
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