I'm thinking that self righting needs be a relationship to how easily is is to knock it down...a narrow deep boat is more easily knocked down (on its side)than a wider shallower and stiffer boat (for the same displacement). It is thusly more easily righted too...but the trade offs must be taken into account...less space, a much easier roll, etc. For every mise there is a compromise...such is the nature of a boat!
Steve