Temps? Humidity? Do you have more than one hide? Is he in a heavily traveled area/loud area or held a lot? How are you controlling the temperature of your heat mat? Heat mats MUST have a thermostat of some kind. How are you measuring your temps?
I cannot imagine a rat's body heat being camouflaged by the heat mat. I've never heard of such a thing. Misses do happen. Some are just clumsy. Some are just bluffing and trying to scare this would be attacker off. This sounds like what is going on so far. Feeding a separate tub is generally frowned upon. It adds unnecessary stress an is often a cause/factor for hunger strikes.