Serge, ON4BAA wrote:
"What about using an inverted 1/4wave groundplane in order to avoid
ground losses?"

How high above the earth can the inverted ground plane be placed?

Brown, of the famous RCA trio of Brown, Lewis. and Epstein, invented the
groundplane antenna. B,L,& E did most of the work on broadcast ground
systems when broadcasting was new. Brown described the purpose of
elevated radials as capture of the antenna current which otherwise might
include the earth which could impose exorbitant loss.

The energy fed to a groundplane produces capacitive (displacement)
current between the vertical radiator and its return paths, be they
radials, other antenna element(s), or the earth.

If you place the groundplane upside down, you lose the screen between
the radiator and the earth, which it hides from the radiator. If the
groundplane is very high, capacitance between the radiator and the earth
will be very small. Likewise, current between the radiator and the earth
will be very small. So, the question of how high can the groundplane
antenna be elevated is not entirely facetious.

Loss is likely lower in the rightside up groundplane

Best regards, Richard Harrison, KB5WZI