Question: How RSSI measured in mesh?
Product and Software: This article applies to Aruba Mobility Controllers and ArubaOS 3.2.x and later.
The RSSI for mesh is an average of the last 10 management frames.
The mesh topology is updated periodically and gives RSSI the mesh-point sees from its parent. This is probably why you do not see much change, because it is updated slowly as shown by 'last update'.
The 'show ap mesh neighbors' command gives the current state, that is, it is read from the AP and gives RSSI from each neighbor listed. You can use this to get the RSSI a portal sees from its children.
ARM is not supported on mesh radios, though it does work on the access radio.