How could Poles from Kresy be enough to repopulate entire regions of Poland?

Question

After the second World War, Poland's borders moved about 200km to the west due to the demands of Stalin. Poles located in the east of their country had to resettle to the western lands newly "acquired" from Germany. Areas which were repopulated by Poles from the formerly-eastern polish regions (also called Kresy) include:

• Warsaw, whose population was almost entirely decimated during the war
• Gdańsk, who only had a small minority of ~10% Polish people during the war
• Szczecin and Pomerania, which was entirely German before the war
• Mazuria, although there was people speaking a Polish dialect most of them considered themselves German so they had to leave
• Eastern Brandeburg
• Most of Silesia, including it's former capital Wrocław

In addition to that, many places which were already in pre-war Poland were completely burned-down by Nazis so they had to be re-populated as well, such as Warsaw. Those repopulated regions were very large close to 1/3 of modern Poland, and include 4 major cities (Warsaw, Gdańsk, Szczecin, Wrocław), and even more minor cities.

However, the majority of the Kresy were already populated by Bielarussian and Ukrainians prior to the war. Poles were already in minority in those regions, except in cities. So people who could resettle those lands came from:

• Wilno
• Lwów
• Minor cities

I fail to see how could people from 2 major cities could suffice repopulate 4 major cities

(This question is purposely similar to my previous question about sudetenland)

Answer 1

It is worth noting that during the Second Polish Republic, Vilno and Lvov were the third and sixth largest cities in the country, with between 200,000-300,000 people. Gdańsk, Szczecin, and Wrocław had much smaller (Polish) populations before the war, so it didn't take much to "repopulate" the Polish populations of those cities (low tens of thousands). They had the advantage of being able to occupy formerly German homes.

For comparison purposes, Gdynia had about 120,000 and Thorn 60,000 in 1938, both of which were decidedly smaller than Lvov and Vilno. (The first two were Polish cities with larger Polish populations than the three repopulated cities.)

And Warsaw was Warsaw. Even if "decimated" meant losing 60%+ of its prewar population (the one third Jewish part and a comparable number of Poles), what was left (300,000-400,000) would be sufficient to repopulate it, because it was still Poland's largest city by population.