Sounds like you need to move the CG back, AND reduce the elevator throw at the same time. It's normal for the elevator to become more sensitive as the CG goes back, but that doesn't mean it's as back as it should be. 4-1/2" back on a 15" wing is less than 33% of the chord.

Decalage is the angle between the wing and the horizontal stab. But you said you had everything 0-0-0, so that's not the problem. (assuming no warps, and you accurately measured the 0-0-0 alignment of engine-wing-stab).