Another thing you could try is to leave the nitro out of the mix. At those compression ratios, they should run well without nitro in this case I believe. However, I think you will probably find max power by lowering the compression as you say, and leaving in the nitro. It will be interesting to see if any additives you try will "play friendly" with the glow plugs...

Another thing to consider of course, is the exhaust timing. Do those engines have "room" for more exhaust timing. If the exhaust timing is low, consider running it up to around 160 degrees to lower the effective compression ratio a bit, gain power, and possibly run ok on this fuel mix. Much over 160 is getting into tuned pipe territory on the exhaust timing.

Just so everyone has all the info possible, altitude, barometric pressure, temperature, and to a lesser extent humidity also affect "glow timing" and compression. An engine that is overcompressed at sea level for example, may not be at higher altitudes.

It was a common "trick" of mine to advance the timing on cars I tuned that remained at higher altitudes. They wouldn't ping, and had better power and throttle response. I've also had glow engines that would tolerate for example, 15% nitro at a field elevation of 4500 feet, but not when run later at sea level....

AV8T0R