Thanks, Crab. I realised this morning that the R22 has camber in the blades now. It used to be 63012 symmetrical aerofoils, so i guess it's now 63212.
This means pitching moment will change with AOA, hence speed. That explains the lateral force trim. Much more and hydraulics (or electric actuators) would get a look in.
Still not sure about the longitudinal bungee though. This seems to imply there is a constant out of trim fore-aft force...