Richard Clark wrote:
"The Thevenin model only requires an IMPEDANCE."

Yes, but "To secure maximum power output from a generator whose emf and
whose internal impedance are constant, the load must have an impedance
equal to the conjugate of the generator`s internal impedance." (page 43,
"Transmission Lines, Antennas, and Wave Guides", King, Mimno, and Wing)

Best regards, Richard Harrison, KB5WZI