Uromastyx basking spot temps

I have a flat stone for my Uros to bask on. I have an infrared heat lamp that gets the surface of the stone to about 112-120 degrees in the hottest spot. My question is: Is this hot enough? I mean do you go strictly by temperature, or do you use the behavior of your animals as a guide? In other words, I realize that I should raise the temperature for my basking spot based on my temperature readings, but as I observe my lizards, they seem to be doing fine in the basking spot as it is now. They climb onto the rock, lower their bellies tight to the surface, and bask for about 5 minutes at a time. When 5 minutes are up, they usually climb down from the spot and go about their business for a while: Cruising, eating, digging, checking things out for 10 to 15 minutes, then going back up to the basking spot for another 5 minutes or so. Also, they usually don't get right under the hottest spot on the rock, just off to the side a little bit. My point is, by my OBSERVATIONS, it seems like my Uros are getting plenty of heat from their basking spot. But by pure numbers (TEMPERATURE) some might say I need to raise the temperature on my basking area. Any advise?

Wayne