Voltage Leaking

Voltage leaking or energy loss reduces efficiency of production of HHO.
Thats a given, when more energy is available than needed which it is when used in a car, care should be taken to control the amps being used, and the amps being wasted (leaked) that just create heat.
I have no idea how to tell what [...]

Control the amps

Controlling the amps has many variables, the most effective is probably the catalyst, adjust the concentration to the amp range you are shooting for.
Try adding Neutral plates, one at a time, these also are claimed to reduce heat produced. Some claim they reduce output, some claim they increase output. Try it yourself and decide.
Pulse modulation [...]