You might be mixing dc-theory with rf, and looking for a particular
relationship that's not there. The antenna is not 100' higher electrically
as you suggest. In terms of your 100' ground rod, just because it might
take
that deep a hole to achieve say, 5 ohms dc-resistance, that does not make
the surface or an antenna above it at an elevated potential with respect
to
each other.

A dipole certainly behaves differently over varying resistances of soils.
But the efficiency differences have never been equivalent to the antenna
being at a different elevation because of soil conditions. Now maybe I get
away with less ground loss from a half-wave dipole that is not quite a
half-wave above ground, because my soil is very sandy, is that what you
meant? It doesn't change the electrical height of my antenna any, but the
soil is such a lousy conductor that less is absorbed by a slightly too-low
antenna.

Jack

You're probably right - but then why does the operator on the hill get
better recption than the one in the valley.
if sand is an insulator, then being on top of a 100-ft pile of sand would be
like at the topp of a glass tower, right?
why not?