Hi Robert,
1. You need to make sure before deployment antenna should be mounted clear of any obstructions to the sides of the radiating elements. Generally, the higher an antenna is above the floor, the better it performs so no worry about high, If possible, find a mounting place directly above your wireless device to ensure the lead-in cable can be as short as possible.
2. Go through below document and see the Elevation and Azimuth plane and mount your antenna as per you site coverage requirement.
http://www.cisco.com/c/en/us/td/docs/wireless/antenna/installation/guide/ant2544v4m-r.html#wp43294