The attachment point for the seat stays can be shifted up or down the seat tube by changing the value for E. But the seat stays don't have to attach to the seat tube. Instead, you can choose to attach them some distance from the top of the head tube, some distance from the rear end of the top tube or some distance from the rear of the down tube. An enhancement in BikeCAD version 11.5 is the option to attach the stays to the seat tube pinch boss. Miter templates can be generated for any of these scenarios. For example, here we have miter templates for a pair of seat stays attaching to the seat tube pinch boss.