The fluctuation has little to do with the equipment. It has everything to do with the environment it is being measured in. Most likey you need to reduce the power on your access points, because you have too much coverage. Co-channel interference and collisions are probably the culprit here. The Airmagnet survey gives clues about coverage, but it does not say specifically what coverage is being provided by what access points, so it does not get to the root of your problem.
Here is what I would do:
The ARM profile by default has a minimum of 18 and a maximum of 127. That is much too high for a warehouse environment where everything is open. RF can propagate hundreds of meters in open space and that can cause exactly what you are observing. I would make the minimum 12 and a maximum of 15, and then take more measurements to see if the "fluctuation" continues.
Access points with ARM do not change channel or power any sooner than 8 minutes, so if there are any fluctuations in power, that is not ARM; that is the environment. Depending on the access point, it can only output power of up to 21 dbm, so a swing of 15 to 20 dbm could not be the hardware, unless the access point is being turned on and off.
If you could overlay where the access points are mounted in the diagram and how high, that would be a good start for us to figure this out...