The most recent test of the E-Cat reports that the E-Cat was operated at a temperature of up to 1,400 degrees Celsius. An E-Cat contains nickel as fuel. Nickel melts at 1,455 °C (2,651 °F). So it appears that there is not very much room for error in the operation of the E-Cat. Trying to make an E-Cat operate at 1,440 °C might induce fluctuations in the operating temperature that can cause the nickel fuel to melt, thereby causing the reactor to stop operating.
Making an E-Cat operate at a higher temperature and therefore at a higher coefficient of performance appears to be a difficult task. This task will probably require a very responsive control system that can take the nickel fuel near to its melting point without allowing the fuel to reach that point.