Hi Tim,

General aerodynamic / hydrodynamic theory is that high-aspect ratio foils will give the same amount of lift with less surface area of board. This equates to less drag, so you get a better lift / drag ratio - that`s why glider wings are long & thin. So assuming you have 0,25sqm of foil area underwater, and the board depth (immersed) is 780mm, that would be the Mozzie standard according to class rules.
If you could lengthen the board, and reduce the chord, you would have a board with the same surface area (lift-generating surface), but the efficiency would increase because you have reduced drag, which would give an increase in lift.
It still amazes me that you go upwind with boards half-way up, perhaps reducing the drag considerably helps to increase the board efficiency.
It gets a lot more complicated than that, my understanding is that this is the basic principle of how it all works. If any of the Engineers / boat designers respond to this post it will get seriously complicated, but I`d love to hear their input.

Cheers
Steve