Parameter-sweeping the endpoints of a waveguide port

I would like to use a parameter to move the impedance line of a waveguide port. I can set the expression but when I update the parameter and press "apply," the port doesn't move.

When i double click on the waveguide port to bring up the ports editor the port updates to the correct location, however. So it seems that applying the parameter update doesn't refresh the waveguide port properties.