D It might well be worth your while to experiment with a simple
D somewhat-directional antenna. A single reflector, located perhaps
D .1 to .2 wavelengths on the mountainside side (sorry :-) of your
D current vertical, cut to perhaps 5% longer than a half-wavelength,
D could be used to shape your antenna's pattern into something
D vaguely cardioid.

Yes! Say, can one just cut the reflector 5% longer than the antenna?
The antenna is some complex double 5/8 wavelength job.
If the reflector is shorter than the antenna, it becomes a director?
What if the reflector is just a pole jabbed into the ground, thus
grounded and longer downwards than the 5%? What if the pole is "very
much longer than the antenna in both directions"?
How about the thickness of the reflector? Only as thick as the antenna
itself (but wait, the antenna has two thicknesses, top thin, bottom
thick), or just grab any iron pipe (wait, metal type and shape
important?)