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Regardless of what plate you use, you'll lose the preciseness and accuracy of the Control Freak... it'll never go above the set temperature but there will be loss of heat from the plate to the cooking vessel. There will never be 100% contact between the two. Now, how much? Depends on the plate and the cooking vessel. It may be pretty minimal. 

Good thing about the Control Freak though is you can learn what works best with your plate and cooking vessel and then program in the temperature. Or just remember the temperature required like I do these days.