Reply: The PZM-185 would be a very good choice for audience miking. If the ceiling is farther from the audience than the walls are, ceiling mounting would give more uniform coverage than wall mounting. Place the mics so that they can "see" the mouths of most of the audience, otherwise the sound might lack clarity. Try a spot centered over the audience with the mics about 4 feet apart.
You could mount the mics on opposite walls, but the stereo spread will be exaggerated so you will need to pan the mics toward the center.
As shown on the PZM-185 data sheet, the mic has a peak in its high-frequency response, so you might want to roll off some highs with your mixer EQ.