I believe you are right  regarding geograpgical basis for it. I forget their names right now, but I am 100% Ashkenazi- one parent is 100% of one variety (the more centralized one), but the other parent has a tiny sliver (2%) that is the descripter that goes further into to Russia. I have a few known closer matches (2, 2c removed 1&2x, 3c) I hadn't marked yet and it picked up those correctly. Once they have that, they might use something else as a plus factor. But there is so much overlap between the areas its not really helpful for research - still so many 2, 3 &4  cousins!. 
  
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Susan Watchman
Phoenix, Az