rcFP

Your problem in inverted flight may be the result of the increased downthrust requiring 'up' trim on elevator - which becomes down elevator when inverted, of course.

With any model the first thing to get right is the CG. First, and easiest, check for this, asuming that the model is not excessive twitchy on elevator input, whihc indicates a CG too far\back, is to climb to height, throttle right back, and put the model into a vertical dive. As soon as the vertical down line is established return the elevator to neutral and observe. For a general sports aerobat you are looking for a straight dive of around 200 feet before the model starts to gently pull out of the dive. A rapid pull out indicates either a too forward CG or excessive difference in the rigging angles of thewing and tail (too much positive on the wing or negative on the tail - same effect). A model which starts to tuck under - going past the vertical - has the CG too far abck. Adjust accordingly.
Once the CG is demonstrably in the ball park, then is the time to start playing around with the thrust line.

Mike