When you say "losing altitude" is the nose dropping and you have to compensate with elevator?

If it's more tail heavy, it will climb while inverted. FYI, with a 46FX, I had to add tail weight and move the battery back to the rear above the servos.

Keep in mind, your plane will definetly fly different when you move the weight around. A super stable plane will become very unstable when you move weight to the back.

Now it will 3D better, just not be as stable for normal flight.

Mike