The resonance of the chamber needs to be tracked and maintained, that is one problem people run into.
In my research, I found that Ozone production could be the key to controlling burn rates. This could also be going on in the GEET with the plasma. By turning some of the HHO into O3(ozone) should slow down the recombination. I even did a little youtube search on the hunch, and found someone who experimentally prove it: