Interconnect Directionality

It actually makes no difference to the argument for wire directionality whether the “energy” of the electromagnetic wave EM travels inside the conductor or outside the conductor. The Poynting vectors argument is a red herring. This is because the material of the conductor and the dielectric determine the nature of the electromagnetic wave, including velocity. The conductor is not irrelevant. That is why the velocity of the EM wave in copper wire is different from the velocity of the EM wave in other materials, including free space where it’s equal to c.

This relationship between EM wave propagation and the physical material of the conductor also explains why there is an audible difference in wire direction. More to the point, you cannot rule wire directionality because the EM wave travels outside the conductor. Even though the wire may be acting as a “waveguide” the physical composition of the wire affects propagation of the wave, thus the wave itself. Since we know the composition of wire is non-symmetrical, it makes sense that the wave will propagate differently depending on direction of the wire.

Quick Summary of the difference between electron drift velocity and the signal (electromagnetic wave) velocity

“The word electricity refers generally to the movement of electrons (or other charge carriers) through a conductor in the presence of potential and an electric field. The speed of this flow has multiple meanings. In everyday electrical and electronic devices, the signals or energy travel as electromagnetic waves typically on the order of 50%–99% of the speed of light, while the electrons themselves move (drift) much more slowly.

The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave traveling along (guided by) the cable. i.e. a cable is a form of a waveguide. The propagation of the wave is affected by the interaction with the material(s) in and surrounding the cable, caused by the presence of electric charge carriers (interacting with the electric field component) and magnetic dipoles (interacting with the magnetic field component). These interactions are typically described using mean field theory by the permeability and the permittivity of the materials involved. The energy/signal usually flows overwhelmingly outside the electric conductor of a cable; the purpose of the conductor is thus not to conduct energy, but to guide the energy-carrying wave.[1]:360”