Optimal tiller toe-in angle is determined from the boat circulation radius on the turn. Many factors influence this circulation radius - hull shape, catamaran drift, with or without centreboards, distance between the hulls, catamaran length, skipper technics of the turn etc..

Very simple example considering only some points:
Circulation radius = 5m, catamaran hull length = 5,5m ; width 2,5m tiller toe-in angle would be 5.4 degrees.
If circulation radius = 6m, then tiller toe-in angle would be 4,2 degrees.
So it is recommended to make calculations for every catamaran and sailor.