If you turn the boat on its side and put the board in, as you push down on it, it will rock on the knuckle in the slot opening so that the leading edge stays where it is but the trailing edge will move to leeward.
This is well demostrated by the handsome bloke in the yachts and yachting test on the nacra europe website.
the movement is only slight at the exit from the hull, but because the board stays fixed at the top of the hull, it is in effect twisting with a greater angle of attack at the tip.
This angle of attack creates lift to windward.
No need to raise the windward board because it is doing the same.
The downside is that you will get more twist on a windy day when you perhaps want less.
i wish that I had kept my old boards and use the new ones on windy days.