Cisco Aironet Series 1700/2700/3700 Access Point Deployment Guide
Cisco Aironet Series 3700 Access Point
Figure 52
In Areas where High Amounts of Metal are Present, a Site Survey is Required
When using 802.11n rates in areas with high metal, such as distribution areas or airport hangars sometimes, lower gain antennas
(on the ceiling) can perform better because they tend to radiate the signal in all directions increasing the chance that multi-path
will enhance the signal. Of course, if you have a clear shot, a patch antenna at the end of an aisle at roughly the same height or
just above the (WLAN client) is preferred.