You may have an air leak elsewhere in the remote needle valve assembly. I had a lot of trouble with my OS .91FX until I finally went to a K&B remote needle valve assembly. This solved my leaning out in the air problem.

As for compression, it's supposed ot be that way. ABC type engines have a tapered brass sleeve that has greater expansion than the silicon-doped aluminum piston. When hot, the engine loosens up. ABC type engines are not known to be good hot restarting engines when flipped. When the engine cools down, the tight compression comes back.

When Super Tigre invented the ABC technology, it was for control line speed engines and was specifically to keep them from seizing up during a lean, hot run.

Some final thoughts on the OS needle problem. I have heard the leaning out problem described as an air leak, as being caused by vibration since the needle is attached to the back plate and because heat from the engine vaporizes the fuel. I don't know for sure what it is. A remote, not on the engine, needle assembly cured mine. I have also read in this forum that the plastic needle assembly from OS also cures the problem.