Is your elevator trim centered with the stab and wing at 0 deg? I am guessing that you have a little down elevator? or your stab and wing are slightly off (wing pos or stab neg)

if you have a bit of down trim, and its good right side up, then climbs inverted... thats the CG. Its aft. When I fly far aft, I set the trims at zero, and just plan on a climb right side up and inverted.

if the wing is a little off of zero, then youcan adjust both ailerons up or down slightly... but then you have camber, and it'll fly different inverted anyhow...