What band are these clients on?
5Ghz
What channel width are you running?
Default
How high are your access points mounted?
about 4 meters (13 ft)
How far apart are your access points mounted?
There are quite a few APs. But one AP's position the distance from device is about ~11,15,19 meters (~ 36, 45, 62 ft.)
What kind of structure is it? (office building, open floor plan, warehouse)
Office building, we have them on two floors, but the upper floor ones don't reach through since it is a heavy concrete structure.
The reseller provided us with Ekahau solution for AP planning.