@Harpers Tate I've got another update I'm just testing which improves alter-ego of alter-ego reporting. But I'm not sure if it is in a useful direction for you.
@Xon
Thanks for attending to the cookie lifespan.
Not a problem! I've set this to 10 years personally, as I boggle at people keeping their devices for that long. At worse I'll make an update which will cause the cookie to be re-set with a new expiry date.
This would be instead of simply suppressing all subsequent reports automatically (which is what I presume you mean by "Only 1 report per alter ego pair made").
Correct.
I suppose that this would be a case of us marking the pair (effectively) "already reported" manually rather than it happening automatically which is what I presume is presently the case.
The system gives you the option to supress duplicate reports for the same pair by report state.

So for example; you can have Assigned/Resolved not bump the report. But allow Open/Rejected to bump it to the top. Or perhaps allow only Rejected to bump it.
I'd prefer to do this manually because I see three possible match types:
1: The pair is honest and genuine. In which case I want it suppressed. (Let me mark it as suppressed).
2: The pair is dishonest. In which case, I'll take some action (eg a ban) and I'm done with it so I'll file the report as complete. However, future reports do not want suppressing in case of - oh, I dunno - the ban being lifted after an appeal, or somesuch. (I won't mark it)
3: Inconclusive. Research is complete but nothing certain one way or the other. I don't want the report remaining in the "inbox", but equally I don't want to lose sight of the pair. In which case I want to carry on getting reports so I can research again. (Again - I won't mark it).
I see this sort of investigation on my own sites, and definitely want to accommodate it.
For more rationale as to why this needs to be the exact PAIR and not any individual accounr permission, there is a discussion in posts 260 and onwards in the thread:
https://xenforo.com/community/threads/alter-ego-detector.60972/page-14
There is a wrinkle in how I've improved/fixed the alter-ego of alter-ego reporting.
Fundamentally, this addon needs to pick a user to peg the reports to. It picks the lowest user id and tries to assign reports to it. This forward only linking is problematic, and may require the addon to add a comment to the other report if it exists.
Changing this will require a fairly significant redesign, as I need to make the addon itself aware of all aspects of the alter-ego relationships rather than hacking it into the report. This will also reduce how much spam the PM and Thread reporting options create. I'm not sure about when I can scheduling that sort of large rewrite in.
For example; given 4 accounts.
5 accounts, but generating a reference between xon2 -> xon4
Now what the 'xon2 has 2 alter egos!' report looks like:
Note; it only adds users to the list of alter egos detected for the first account once.