Yuri, K3BU wrote:
"I can see conductor (assuming insulated wire) having its electrical
length affected by the capacitance between wire and earth, but wouldn`t
current stay close to same along the length?"

Depends on distance from the source. Current fades fast close to the
source, but at a great distance, the decline is very slow.

Traveling waves don`t require a complete electrical circuit for
propagation. They travel well in a complete void. So, the volts and amps
far from the wave source don`t need to equal those at the source.

V=frequency times wavelength always prevails. So, capacitance between
wire and earth for a given frequency changes the wavelength because the
velocity of the wave is changed (slowed) by proximity of the earth.

As a traveling wave is free to be attenuated in travel, current must
decline enroute. Brown, Lewis, & Epstein, the 20th Century RCA geniuses,
declared that the place to end extending ground radials is where their
current becomes insignificant.

Yuri also wrote:
"Why do we use radials if the conductors become lossy?"
Yuri also had answered the question before asking. Didn`t Johnny Carson
patent that routine, holding the question envelope to his head while he
gave the answer?
Yuti`s answer: "Wire and dirt, with less resistance wire taking over."

Yuri also wrote:
"Why does the Beverage laid on the ground work?"

Kraus says a wave traveling along a perfect conductor produces an
electric field perpendicular to the conducting surface, but along the
earth the electric field has a forward tilt. The horizontal component of
the vertical wave produced by the tilt is associated with that part of
the wave that enters the surface and is dissipated as heat. The vertical
component of the wave continues to travel along the surface. The emfs
induced along the antenna by the horizontal component made of the tilt,
all add up in the same phase at the receiver. Maximum response is in the
direction of the horizontal wire.

Best regards, Richard Harrison, KB5WZI