Hello, I read a care sheet on tomato frogs and it does seem that they bury themselves. So ya putting on the bottom may not be wise. Most of these burying frogs do this to cool themselves and to get out of the direct sunlight. So if it is on the bottom he may not be able to regulate his body temperature properly because he wont be able to cool when he buries himself, hopefully I said that properly. L.O.L So if your going to use a UTH you should place it on the side or the back, and a little tip if you have the small 10-20 gallon UTH don't open and bring it back and get the next size up. That small one isn't going to nothing for you, and the next size up will be to big for the side so put it on the back. I use 2 in the winter to keep my temps up and I have a small 10-20 on the end and a 30-40 on the back and they are placed so they almost touch. I don't know how cold it is were you live but you may only need the big one on the back, and I did this for my pacman frog. The warm end hits 84f, the middle sits at 80f and the far end is 78F and these are day time temps and then at night I dim the big UTH and everything drops about 3 degrees. This way he can move through out his tank during the day and night to were the temps make him more comfortable. Or you can go easy the route and get a Ceramic heat emitter or some lights. hope this helped abit.