The intent is to get the fell to the "horizontal center" of the rump, which should be 1/3 of the way down on a proper length kilt. Any higher and the rump "pulls" the pleats. Any lower and it doesn't "move" right (it is too "stiff" below the rump). At least that is my understanding/opinion. The proper way to "dart"/shape/(I forget the correct name-> tired) the fells varies depending on the shape of the rump lower back region and the number/spacing of pleats