As the topic name states already 
What’s the best orientation and position for the AP6 and AP6 pro? And can that answer be supported based on documentation and or specs?
Would definitely go ceiling mount if you are covering multiple rooms. There is a -10db or more signal loss on 5ghz on the backside of the device on the Pro. Not as much on the regular AP6 but that one does have a nearly -15db loss right at the backside centerline.
-10db can make a big difference.
2 Likes