Applied Power on TVS Diode
Yes. You are right.  

In simple terms power dissipation is simply the product of the applied reverse voltage and the reverse leakage current.   

The reverse leakage current varies exponentially with the temperature. Hence the power dissipation will be proportional to the temperature.   

Here is one Example of computing reverse losses in a diode in a typical application.
Another example from one of the TVS diode datasheet from Vishay:    

For simplicity, you can take worst case reverse leakage current and reverse voltage to get power dissipation during normal operation.