The T value which determines the length of the tapered section on a chain stay or seat stay will be disabled if you opt to curve the tube in the side view. This is because tapers will be arranged to coincide with the bends in the tube.

Meanwhile, I have not been able to reproduce the issue you've reported with the VR dimension. Could you e-mail me a BCAD file where you've observed this problem? One possible explanation might be that you are unaware that VR controls the diameter of the stay in the side view, but HR controls the diameter of the stay in the auxiliary view. This allows you to specificy an elliptical cross section for the stay. Is this the source of confusion?