When moving the boards back, you also rake the mast aft to load up both boards and rudders to get that shared lift.
One theory is to use the boards for lift and then the rudders just steer the boat.., this is the way things were for years.
Then folks started raking masts aft, copying the Hobie 16, to put load on the rudders as well.
At first it was not particularly effective.., probably because we were not using enough aft rake.

Wouter mentioned the Wave which sails very high to windward with only a skep. But, the mast is raked way aft to utilize the skeg and the rudders for underwater lift.
Rick