hey,
My beardie tank is really big and has tiles on the bottom, but I put sand ontop of that, but sometimes use the tiles without the sand for some areas of the tank. My tiles are probably bout 1 foot squared i guess.
these pics are pretty old (and those beardies are a lot bigger) but yeah, the tiles are underneath the sand.
doesnt get too cold, but my tiles are sorta rough, not like bathroom tiles. If you want I can take a pic of one.