New home made cages but problem regulating the heat.

[lennycorn]

I finish making some new cages as you can see, using flexwatt. I'm using Repitemp 500R to control it but because the cages are "stacked". The top one is about ten degree warmer that the other. I move the probe of the 500R to the lower cage but after a half a day I get the same reading, the lower cages cooler by ten or so degrees. They are bult the same. I'm just wondering....Am I missing something?? Or do I just need to get a better thermostat?
Thanks