Does anyone know how do GKs work? What attribute(s) does a GK use to get better at catching balls? Obviously, GK special abilities help, but is that all?

What makes a 5 stars GK better than a 2 stars one? Aside from his greater stamina, because of his higher Strength, of course.

Is this info known to the general public, or it's another one of the countless unknown things Nordeus just won't comment on?

Thanks.