Don Gillies wrote:
"---none of these has explained where the two points are that the
voltage is being measured between."

Kraus calls the potentials near and far from antennas "retarded
potentials", involving t-r/c, where t is time, r is distance from the
origin, and c is the speed of light in free space.

On the conductor itself, the origin would seem logical as a reference
point for antenna voltage. Antennas are often considered as extensions
of the feedline,

Feedpoint rms voltage is simply the potential between the wires at that
point. Instantaneous volts depend on phase along the antenna, impedance,
reflection, mutual coupling, radiation, and loss.

Best regards, Richard Harrison, KB5WZI