The main reason a high impedance feedline equals lower loss is that the
resistance in the feedline is the main loser. Its loss is current
squared times the total resistance. The same power can be conveyed as a
high voltage and a low current (high impedance), or as a low voltage and
a high current (low impedance).

When conveyed as a high current and a low voltage, the power extracted
by resistance is higher for a given power conveyence. Powerline voltages
are often limited by flashover voltage. That`s a reason for d-c
high-voltage power transmission. D-C is at peak value all of the time,
and needs to be insulated for no higher voltage. Maximum voltage means
minimum current for a given power. Ciurrent squared times the resistance
is lowest too.

Loss increases with line length for a particular cross section. A
rule-of-thumb for powerlines is that your transmission voltage should be
1000 volts per mile the energy is to be transported.

Power is volts x amps x cos theta. Cos theta is the power factor which
should be 1 to minimize total current (zero reactive current). Impedance
of the line is volts / amps.

Best regards, Richard Harrison, KB5WZI