Pripet should be impassable for all but infantry. Beyond dispute there were areas where armour or heavy artillery could not effectively operate, and further types of terrain where they had a distinct disadvantage versus infantry (e.g. mountainous areas.)
I believe there is room in A&A for 3 or 4 basic terrain types with different effects; after all planning an invasion of France should be very different from landing in Norway.
Even the simplest wargames have lowland and highlan/difficult terrain, which can have a profound effect on strategy. In a game supposedly set in the real world it’s yet another factor that, properly implemented yet with simple rules, could help produce a playout that feels more like real events.
Note that I make Turkey in Asia and in Europe one territory, controlling passage through the straits. Likewise Panama and Egypt; don’t know why they insist on Trans-Jordan co-controlling Suez.
Thinking about compiling a list of potential “partisan areas”, e.g. Alpine Redoubt (German Werewolves), Balkans (Yugoslavs), Rocky Mountains, Scottish Highlands etc, but probably only the Soviet/Pripet combination represents something likeley to have a measurable effect at the level of A&A.