Ron, K0QVF wrote:
"How far from the tower should I mount the antenna?"

Supposing you want the least effect on the pattern and impedance, place
the antenna as far as possible from the tower.. Satisfaction is obtained
with much closer spacing. The tower is non-resonant. Its reactance will
impede induced current from a radiator which is really close by. If
there is little induced current there is little re-radiated energy to
foul the pattern.

The 3rd edition of Kraus` "Antennas" has a graph on page 350 of gain in
field intensity versus spacing from a flat reflector. At 0.5 wavelength
the gain is 0 dBi. That`s less than the resonant 1/2-wave antenna alone
which has about 2.14 dB gain over an isotropic.

The graph shows a gain of about 2.14 dBi with a spacing of only 0.1
wavelength spacing. So, anything greater than 0.1 wavelength from the
tower should be fine. That`s 20 cm in the 2-meter band, or about 8
inches. More distance means less coupling and should be better.

Best regards, Richard Harrison, KB5WZI