I think I have this wrong, I have given advice I think for weather helm, ie your having to pull the tiller towards you more to keep the boat from luffing into wind.
You say in your text that you are moving the mast aft, ie, more rake. That I think is to reduce Weather Helm not Lee Helm.
Also when raking a mast aft, the heel needs to go forward as your pivoting about the pin
Maybe you can say what your finding your having to do with the helm and we could then work out which helm you have.
Could also be that I am going off my rocker,but lets not get the shape of the keel into this!!