Dr Lodge said:But if you think of the impedence of the cable as a combination of resistance, capacitance and inductance and draw a simple diagram using one of each, then the capacitor that spans the two conductors must be either in front of or behind the inductor which is in series with one of the inductors. This model is not symmetrical which implies direction does matter.
I am not sure about this... If you reverse the signal direction, you reverse the diagram/model as well (because the model must represent the behaviour of the cable)?