distance of mast step relative to keel fin LE

after viewing and studying closely zillions of pics of different IOM designs, i noticed that wide beam designs tend to have the mast step much nearer to the keel fin LE, and narrow beam designs seem to have the mast stepped much more forward of the keel LE. i know that this has something to do with the CE/CLR thingy but is there a general rule of thumb when balancing a wide/narrow hull? and location of fin LE, e.g 50% of LWL?