Jim's method is what I use except on 23&Me.  In my experience every set of matches has at least one segment where a lot of people match.  I haven't figured out if this is a real effect or not.  The one  projected 4th cousin (actually 5th once or twice removed since I match to his grandmother also and at the 5th cousin level) thinks our match is something about an ancient segment which makes no sense to me. But I'm really writing about my biggest log jam (about 30 people on c 18).  EVERYONE at that site matches several other people from that segment somewhere on their DNA and usually multiple times.  The longest match to me is 15 cM; the shortest is 7.  23 projects the nearest cousin to be a 4th cousin and the most distant a Distant cousin.  I looked at the overlaps yesterday; and the failures of matching each other at that same segment could be entirely accounted for by one person's true ending being at an unfortunate place .  Occasionally one of those segments would appear to be lengthened by the IBS mechanism by about 10% but only very occasionally.   About a third of the people have reported somewhere Ashkenazi roots.  All have roots within about 300 miles of the  3 country point of Ukraine, Poland and Belarus (I'm about the furthest). The one 4th cousin had been briefly downgraded from 5th to Distant when 23 implemented their first algorithm for lowering estimates for Ashkenazi rooted people but then back upgraded to 4th. Bottom line: I now know for sure that all 30 can match each other consistently on that segment although with that 10% lower estimates of length for some. I haven't figured out yet the total number from  the rest of my matches who have multiple cousins in this list.  But all my first 4 pages (at 25/page) have cousins in 1 of 3 lists.