You may want to try modifying your plates to accomodate a solid nut and bolt config. The heat is building up due to resistance in the connections from your terminals to the plates.
Electricity flows like water in a garden hose. Putting your thumb over the end of the hose causes the water to come out faster and well, the pressure that your finger feels translates into heat within the path of electricity.
The power is conducted through the terminals and is being forced into a different size "hose" in its travels to the plates. By connecting solid nut and bolt hardware to your plates, and using them as the terminals should eliminate the excess heat you are getting.
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