First realize that the boards and rudders are essentially the same thing just in a different location. They both share the load from the sail plan. How much load is on each of them depends on the position of the sail plan in relationship to the foils. When you move the sail plan aft (more rake), the rudders begin to carry more load.

Getting the balance right between weather/neutral/lee helm is not an issue of right or wrong for the sail plan. Adjust the rig/sails for max performance. Then once you know where your rig needs to be, you adjust the rudders to match that setting.

As you rake the mast aft, the rudders begin to carry more load. What you feel in the helm as weather or lee helm is simply an issue of imbalance. If the boards are carrying 70% of the total from the main, then the rudders would be carrying the remaining 30% (assume 0% for the hull to simplify argument).

The total quantity of lift for the entire board can be averaged and assumed to come from one spot on the board, the CL(center of lift). The lift from the foil and from the sails can all be assumed to be concentrated on this point (one for each of the sails and boards). The rudder is the only one that you notice a change in because it is the only one that pivots and we are directly connected to.

Here is where the balance comes in. The quantity of lift and it's relationship to the piviot point of the rudder is why you feel weather or lee helm. It isn't an issue of more leverage against the rudders. It is that the CL is either too far forward or aft of the pivot point of the rudder. As the rudder is raked, the loading does not go away, it is however carried by a different part of the boat. Instead of being translated to the skipper and him/her haveing to pull on the stick to keep the rudders straight, the pin is now carrying the lateral load and is experienceing more sheer stress. You have simply found the point where the CL is aligned with the rudder pin and the forces balance.

On additonal thought...it is in a way a leverage issue. By raking the rudders forward, you decrease the leverage the rudders have on you (shorten the distance between the CL and the pivot). This is a fix for weather helm, so long as you are not having to keep the rudders turned to keep the boat going straight.