The way i am pretty certain thsi all works is through the wings on the rudder. I think there is a bit of a gearing effect going on, whereby for any given increase in speed, the lift from the rudder increases at a higher rate than the lift from the main foil. This means that as the boat speeds up, the back lifts quicker, reducing the angle of attack of the main foil and this controlling the amount of lift.
Humm, it could be the contrary.
In your explanation:
- the more speed the less lift on the front of the boat, in fact we want the contrary. Not to say that yours can't be right, but you would push too much water in medium.
- if you have a look at the last picture of the rudder (the one with a winglet in the middle of the rudder) you will notice a few white line that seem to indicate a neutral position and even a negative one (the planes work like that)
So, I think that:
- the rudder provides a moderate lift. The lift will be minimum, as set for high wind, knowing it only be a minor drag in light wind.
- the main foil provides a positive lift vs the rudder one, and it can be adjusted with the depth of the dagger board.
The control would be done by the twist of the sail and the depth of the main foil, the higher the wind, the higher the foil.
The diffculty being to adjust the differential between the two foils, which would explain the little with lines on the rudder. Whatever the explanation is right, something is sure, they fine tune the balance with the rudder foil and not the main.