I don't know it this will help at all, but from experience in the full size extra 300 the plane actually pitches up toward the canopy during knige egde.... It almost sounds like downthrust is causing your pitch down. If it's not downthrust then it is aerodynamic, probably has to do with the flow over the fuselage at high angles of side slip, or beta. For example the bottom of the cowling is much more curved then the top so it stands to reason that the pressure would be lower on the bottom of the cowling then on top causing a downward pitching moment... same goes for the aft fuselage... why I don't see this in the full size extra, who knows.

Ty