Many times, 2-cycle stunt engines respond best to a combination where it burns a LOT of fuel, especially where you are flying in competition and need to control run-time very carefully. The more fuel loaded, the less precise the measurement needs to be. Plus, the engines often are just happier getting more fuel
and more oil through them. I'd expect every engine would be different in its needs.
If I lived where I couldn't get nitro, I'd expect to run a bigger venturi and more oil (especially more castor) in the fuel. I think Brian Hampton wrote about having a terrible result with the G.51 until he changed to 25% castor??? That would increase the fuel burned for a given flight time. When I flew CL Speed, I mixed my own fuel, and discovered that 65% nitro ran the same rpm, whether it was 15%, 20% or 25% oil (synthetic). I thought less oil should run faster, but it didn't. I didn't think about run time, but should have found that 25% ran shorter, and 15% ran longer.
For sport flying, I'd suggest trying zero nitro and see what happens and how you like it.
Steve