Has anyone come across 2x2 standard ceiling vents that have RF dampening qualities? I work in a large, newly constructed, 4 story Hospital building that has, in some areas, as many as 6 2x2 air ducts all in a row. I get severe RF bleed from other floors. This causes areas of co-channel interference on the b band that cause havoc on spectralink phones passing these areas. I have the AP transmit power dialed down as far as I can (8 to 10 dBm). Any assistance would be greatly appreciated.
I would bet that better grounding along the length of your ductwork would help tremendously.
Check out the requirements for Tempest and Zone level approved installations too.
Try higher gain omni antennas. The higher the gain, the flatter the vertical beamwidth. It's a trick that quite a few of us use, back when I used omni antennas. :)