Re: Top results with Castor @ 30%
Based on your observations, castor may be a good choice for these primitive engines. I have a 4 cycle and love it.
The only other comment I would have is to watch the carbon build up in the ring lands. Two cycles are known to snap rings due to carbon build up and the castor oil is notorious for creating that build up.
If it works great for you, that's certainly good enough reason to continue to use it!