"Cecil Moore" wrote
The average gain of a 1/4WL vertical monopole
with ground-mounted radials is in the ballpark
of 0 dB in all directions.

It is extremely difficult, if not impossible,
for a vertical monopole to achieve 6 dB gain
in any direction.
____________

Zero or six decibels with respect to what reference, Cecil?

If that reference is an isotropic radiator, then note that a typical
1/4-wave monopole and buried radial ground system used by commercial,
non-directional AM broadcast stations has an h-plane gain of about 5 dBi.
This value has been confirmed by thousands of groundwave field strength
measurements of such systems going back 70+ years. Also note that the gain
of this monopole over a perfect, infinite ground plane would be only 5.15
dBi, so a broadcast radiator is quite good indeed.

And -- a gain of more than 6 dBi is produced by broadcast monopoles whose
height exceeds 1/4-wave sufficiently. For example, the h-plane gain of a
1/2-wave broadcast monopole system is about 6.6 dBi (6.8 dBi over a perfect
ground plane).

RF