I recently turned up a 145km link using the B5C over water. The link is good but it keeps trying to go to a higher modulation when possible which in turn makes the link a little unstable. The feature I am suggesting is available on the Cambium PTP650 radio. Essentially, it caps the modulation of the radio to a user defined level.
Also, there is a minimum modulation which will drop the ethernet port on the ‘slave’ radio causing routing protocol to use alternative path if available. This is useful for long links experiencing rain fade or any additional losses to fail automatically to an alternate path.