The wide platform of a cat allows for an open "slot" between the genneher and the mainsail. This accelerates the wind over the back of the mainsail and creates more lift.
Not true, it's been shown that head sails actually do NOT increase the WS in the slot, they actually decrease it. What they do however, is keep the flow attached to the lee side of the main longer/more consistently which improves it's efficiency and therefore it's performance.
