If multiple-head showers are installed in a single shower compartment, the reference guide states that we need to sum their flow rates and enter the result as one fixture. However, if both showerheads can not be used at the same time, this does not make sense. With a main shower + handshower and a setting that you have to choose one OR the other, it would make sense to indicate the flow rate or the showerhead with the highest flowrate instead of using the sum of both showerheads. Does this make sense?