Well first, make sure the hot spot under the RHP isnt too hot using a temp gun. If it is too cool, then the RHP is too small. Also remember, you are trying to heat the floor from 24" up. Thats a lot of work. Might be better off using a combo of flexwatt and RHP or might have to make a shelf under the RHP so its closer to it.

But first thing you have to do is verify the temp on the floor directly under the RHP. Right now your temp reading is coming from the spot where the probe is.