I have a great planes Reactor 40 size, equipped w/os 55ax. It takes quite a bit of down elevator for level inverted flight.
The CG is a little aft of recommended. Anyone have any ideas why it would take so much elevator.?? Maybe its normal.??
Thanks
Brian

Try adding a little down thrust in the motor by added a washer under both rear mounts.

My first guess is that it is nose heavy, since you didn't comment on any other flight characteristics. Try moving the balance a "little more" aft.

I have the same airplane with a FS91SII up front. It requires a bit of down elevator as well. But there are no airplanes that will fly inverted hands free. All airplanes, even aerobatic ones require some down when inverted. Difficult to say how much you require. Mine doesn't require too much, this is the first airplane I was able to do a full circuit inverted comfortably in 5 years of flying

Ameyam