Wouter,
Sailors on a racing beach cat have several things to control. They trim the sails with the sheets. They steer the boat with the helm. They trim the hull out fore and aft by moving their weight forward or aft along the hull and they move their weight athwartship to balance the angle of heel. Which ever team can do these tasks in the best concert usually has the best boat speed.
On the angle of heel point: It doesn't matter how wide the boat is, you always want to barely fly a hull. So if you are on a very wide boat you may not trapeze or you might ever have to sit in the middle of the trampoline to get the hull to fly. In the same wind conditions on a narrow boat the team might be trapezeing to acheive the same goal. The point is to get the most boat speed out of your boat you place your weight where ever you need to to acheive the optimum goal. It is possible to trapeze when you don't need to and that is slow on a wide boat or a narrow boat. It is also possible to overtrim the sails on both boats and that is slow also. The wide boat offers the option to go very fast when the wind blows hard and you can't do that on a narrow boat. I've been there and done that, Wouter.
Bill