I went out one day with a trimmed out freeflight model and a roll of solder. I added solder to the tail between flights. It went from a near vertical climb (under power) to a less steep climb to level fight and I even got it into a shallow dive by moving the CG back more and more. I did some calculation of free flight CG, tail volume, etc and came to the conclusion that there is about a 10% range of Mean Average Chord for Cg position ranging from marginally stable to really stable.