It was 20% back in 1989 and sure had a lot of 'mixed' families. In post Soviet Ukraine and Belarus such people choose to identify as Ukrainian and Belarusian.
But of course you also need to consider the history between the 1600s and 1917.
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I just wonder why Ion stresses Ukrainian-Russian mixing in East/Central Ukraine, but forgets about Polish-Ukrainian mixing for 7 centuries (1300s-1900s) in West/Central Ukraine.
Kubiyovych wrote about Ukrainization of Poles (although the opposite process - Polonization of Ukrainians - was more common until 1939):
https://i.imgur.com/sbQ8U7W.png
https://i.imgur.com/oiuehUE.png
Surprised to see so much northern people in Zakarpatia, some score 46-47 Baltic, and this is near Romania.
Frankly some of those Kiev samples do look like mixed individuals or outliers. I'm removing them from my Dodecad average.
BTW, Lviv / Lwów / Lemberg was originally a largely German-speaking, Ostsiedlung Stadt. Later they all became Slavicized (Polonized, some Ukrainized).
Maybe he is connected to these guys, they lived in the region 300 years ago. This is the first thing who came in my mind to explain his results.