So my conclusion is that even though the vertical might have the low angle
pattern, the losses in the soil do not allow the advantages to be realized.
Phased arrays of similar antennas over lossy soil may show the nice pattern
and f/b but the absolute value of gain expected may not be realized.

My experience in MS (clay soil) comparing a dipole (nearly flat-top) at
about 90 feet to verticals is that the verticals nearly always win for dx.
(this is on 3.5 MHz).

However, I usually put down ~50 1/4-wave radials for the verticals.
I would definitely increase the number over 18.

My qth is also surrounded by a large number of large pines. In fact
the verticals I compare to are wires supported by the trees.
I have no idea how much they affect the signal, but verticals still
outperform dipoles for dx at my qth.

Do you have other metal objects or ground clutter (houses, etc) near to
the vertical? What was the feedpoint impedance of the vertical?

Tor
N4OGW