My thoughts about this matter are that some type of bodies are much more "adaptable" to "standard" shotgun dimmensions that others.
Slim and tall bodies adapt very easily to almost any "normal" shotgun. A thin long neck helps a lot to put your dominant eye in the correct place over a wide range of shotgun´s meassures.
Short and fat bodies are the worst in terms of adaptability; big and tall in the middle.

I also think that cast is the most important meassure for gun fitting.

Best,

Jose M. Fernandez