Also depends if you are using external antennas. I have installed access points at 4' level in NEMA enclosures (locked), LMR cable with vertical runs as high as 40 feet. You have to look at the attenna radiation pattern, i.e. you are installing outdoor sector antennas with Azimuth (horizontal beamwidth) of 120 degrees but only a 10 to 20 vertical beamwidth. I covered a flight line once where signal was needed 2000' out, without the correct antenna with proper horizontal beamwidth, it is sort of like aiming a search light to provide coverage. It all comes back to proper site survey and planning for usage and coverage.