"Wimpie" wrote
In real world (average soil and short wave communication), under very
small elevation angle, reflection coefficient is almost 1 and the
phase is 180 (so field cancellation above ground does occur). This is
valid for both H en V polarization. That is why the antenna/ground
combination cannot have its maximum of radiation at 0 degrees
elevation.
______________

One exception being the typical MW broadcast monopole vertical used with
120 buried radials, each 1/4-wave or more in length. This configuration
produces its maximum radiation in the horizontal plane (ie, zero degrees
elevation). If this was not true, then AM broadcast stations would have
very few daytime listeners.

The ground wave fields 0.3 mile from such antenna systems have been
accurately measured as far back as 1937 by Brown, Lewis and Epstein of RCA
Labs, and for a vertical radiator of 60 to 90 degrees in height shown to be
within a few percent of the peak, free-space field produced by a 1/2-wave
dipole, at the same tx power. The frequency used in this set of tests was 3
MHz.

Ground wave propagation loss including earth curvature will cause the
h-plane field from these verticals to go to zero beyond some distance* from
the transmit antenna site, but that does not mean that zero h-plane field
was "launched" by this vertical radiator in the first place.

*and that distance can be over 200 miles for a high power AM station on a
low frequency

RF http://rfry.org