This looks pretty versatile: Ball and Socket for Iris Motion
Before you commit to a bunch of these (or any type, for that matter) it might be worthwhile to try one out. The detection angle is pretty broad and not tightly focused; aim may not be as critical as finding a way to make sure it doesn't see sunlight (to minimize unwanted triggers during daylight hours).
I use my Iris sensors around the perimeter of my house (all under eaves) and false triggering isn't a major issue; the one Z-Wave sensor I use is in the backyard and is there mainly to scare/amuse the deer by turning on a floodlight at night. False triggering in this application is only a problem during some crazy convective weather, so my automation does some rate limiting if triggers get too frequent.
