Examination of the radiation patterns of horizontal HF antennas
(Dipoles, horizontal rhombics, etc.) near the earth confirms that they
invariably have zero response at zero elevation on their best azimuths.
(Should have made it clear that the antennas were near the earth, not
just their patterns.)

The earth reflects energy which strikes it at a grazing incidence
inverting the phase on reflection. The incident and reflected HF
horizontally polarized waves add to zero producing a null along the
earth`s surface.

I did not include enough detail in my earlier posting so Richard Fry
replied:
"If this were true (zero response at zero elevation on their best
azimuths) then most television stations would have zero field strength
near the earth over much of their present coverage areas."

If TV station antennas were 1/2-wavelength or less above the earth,
their field strengths near the earth would truly be near zero over much
of their present coverage areas, VHF, or UHF.

Best regards, Richard Harrison, KB5WZI