Dear Serge,

Yes. But why make such a song and a dance about it.

It's quite obvious a 'ground plane' on the ground, or even shallow-buried,
causes greater losses in the ground than any elevated ground plane. The
greater the elevation the more efficient the antenna becomes. Eventually,
with sufficient height, the efficiency equals that of dipole in free space
whatever the antenna's orientation or form of groundplane it employs.

Have a good holiday.
---
Reg, G4FGQ