That is not why they did it, and system was much more complicated because of ocean of ethnic groups in Soviet army. My father served in Leningrad (he was from south region, from Georgia) near units full of locals mixed with many other ethnic groups.
I happened to meet a Russian tank platoon once, back in the 80's in East Berlin. They were all about 5'0" to 5'6". Except one poor guy who was probably a bit over 6'. He must have had a growth spurt after he was conscripted, because his uniform pant legs and sleeves were about 3 or 4 inches too short. They were also all of Asian descent, except their officer/commissar. The Soviets used to send their Asian conscripts west, and European conscripts east, so they were less likely to sympathize with the locals in case of a rebellion.