I do not think you are going to lose much of your MMW gains by re-opening your bottom holes. The PWM does make gains over straight DC. I have tested it over and over. You will get more effecient as you raise electrolite levels and lower duty cycle. Every time your PWM turns off power there is a revirse electrical spike. Your cell will continue to make HHO during this process. Your best effeciency will come at lower duty cycles.