Stereophile presented microscopic photos of the crystal structure and they were arrow shaped and lined up nose to tail, naturally the arrow head was pointed, and was considered as the flow direction.
>>>>>That’s weird. I would have thought the flow direction would be the opposite, the EM wave would travel more easily - I.e., with less resistance - in the head to tail direction. That direction would present a smoother pathway. Like stroking the quills of a porcupine in the direction of the quill tips, not the opposite direction, against the quill tips.