Jeff,
Try using the AC as a mounting point for a horizontal
bar running out far enough to mount an antenna on, such
as some type of 'base'(?) antenna.
All antennas have to be tuned and/or impedance matched.
Any antenna near obstructions will have undesirable
characteristics compared to the same antenna in the 'clear'.
I think what you're seeing is fairly 'normal' for your
situation. Good luck...
'Doc