The point is also that the German threat was gone after WW2 which was a major factor mentioned in the early talks for the Karelian question in 1939. Even if there was a pact with Stalin and Hitler the Germans were considered the threat in 1939 and not the Allied. But then again Churchill did have dreams of sending the RN to visit the Baltic see and maybe the Gulf of Finland as well...
Also in 1939 the artillery range was considered the reason why the border should be moved. In 1945 with new weapons actually youŽd have to make new changes to the borders to protect Leningrad and even that might not help. ( rockets etc )
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Also, if Stalin only wanted the buffer zone for Leningrad and was forced to take it why did the Red Army attack all along the front in Nov-Dec 1939?
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