I would suggest the following rule: Combining the old rules with the new rules
Finland becomes an Axis minor on the check for minor allies phase on the turn that all of Norway’s territories are Axis occupied or the turn after the Soviet Union and the Axis are at war.
While they were a German ally in WWII, Finland enjoyed a degree of autonomy from German control during the war.
To reflect this, when Finland becomes an Axis minor, the German player rolls a (half d6) + 5 and places it in Finland. The die result represents the number of "German" units that may be in Finland (including Vyborg) and trace supply through Finland.
German units greater than the die result may not occupy Finnish territory (including Vyborg) or trace supply through Finland. If there is an excess of German units supplied via Finland at the conclusion of the non-combat movement phase, it creates a diplomatic challenge making all German units in Finland out of supply and no attacks may be launched by Finnish units or Axis units in or from Finnish territory (including Vyborg) until Leningrad falls to the Axis or if any Soviet Units enter the post Winter War territories.
Additionally, Finnish units may only operate adjacent to the 1939 Finnish-Soviet border (including Leningrad). If Leningrad falls to the Axis or if any Soviet units enter the post Winter War territories that make up Finland (any Finnish territory other than Vyborg), this restriction is lifted an any number of Axis units may enter Finland and Finnish units may operate outside of their adjacent territory restriction.
Germany had not only Mountain divisions in Finnland.
Like the (All together 6 or 7 divisions)
169. Infanterie-Division (Not Mountain)
Two Panzer divisions
The Luftwaffe landed its air divisions in Rovaniemi, Luonetjärvi and Utti.