My thoughts are that the default behaviour in FreeRADIUS should always be:
&Acct-Unique-Session-Id := "%{md5:%{User-Name},%{Acct-Multi-Session-ID},%{Acct-Session-ID},%{%{NAS-IPv6-Address}:-%{NAS-IP-Address}},%{NAS-Identifier}}"
I also should have mentioned before, that the NAS-Port-Id should be dropped too in addition to the NAS-Port.
Those are there for dial-up or DSL concentrators. They're useful for some people, and need to stay in.
You're free to make changes to your local config, of course.
Of course, but that pushes the complexity of understanding all this on the administrator. I wonder if a better approach here would therefore be a configuration ability to easily specify intent somehow and somewhere. Intent being specifying, for typical deployment scenarios, that you're doing wired/wireless 802.1X or instead something with dial-up /DSL concentrators. Different behaviour is optimal in these diverged use case scenarios.