Maximum ground loss during wave reflection, between low resistance sea water
and very high soil resistivities, could very well be when soil impedance is
of the order of 377 ohms. Or is related to that number.

This is because, on the average of incidence angles, soil is more likely to
absorb than reflect wave energy received from free-space. There's a better
impedance match with free space at 377 ohms. The reflection coefficient is
smaller.

Soil permittivity and frequency will also have an effect on the ballpark in
which maximum absorption and hence maximum transmission loss lies.
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Reg, G4FGQ