There is what’s known as "the ideal attitude" for the position of a cat in the water. It is the same for all points of sail, and all wind and sea conditions.
Basically the leeward hull transom should always be just clearing the water at the transition point of the transom and the bottom of the hull (this is so that there is the least drag produced by the movement of that hull through the water). The windward hull should be “flying” only just clear of the water, (once again to reduce drag to its minimum possible). Towards maintaining the hulls in this “ideal” attitude, the moveable “ballast” ,(the crew), positions themselves accordingly. Obviously the positions that a crew have to be in will depend enormously on the prevailing conditions at the time. The control of the sails is the other factor in the “balancing” of the cat. Whenever the hulls change from this attitude, extra “drag” will be induced from the “ideal”, but the object is to attempt to keep the “ideal” as much as possible (or at least more than your opposition) – less drag, more speed (and control).
There is no “set” position for a crew to position themselves in, it will depend on many factors, I.E. the weight of the crew, the point of sail, the longitudinal buoyancy ratio of the particular hulls, the mast rake, etc. so that the position fore and aft and side to side of the boat that the crew position themselves will be solely governed by their need to keep the correct attitude of the hulls in the water for maximum speed and least drag.