Very interesting article. Thanks! Yes, I agree that because your link concerns autosomal dna only, it does belong in the autosomal sub-forum, but who knows why things get moved around here?
Sherlburl, I wonder if this explanation has to do with the actual placement of the matches in the relationship categories. In other words, this Mb measurement is what places a match higher or lower in the groupings. For example, I had 2 third cousin predictions, and when I received a new one, it was placed in the middle of the two. At Ftdna, we can filter our matches by relationship, shared cM, or longest segment. From your blog link, I'm assuming that this placement is Ancestry's filter of high to low. no?
PS I still haven't been able to find our match. In light of your link, this may be something I need to look at. :)