I only do 2 inf 2 art 2 arm if I’m going to mess with Ukraine on USSR1 or USSR2. For that plan, you want to have attacking units on the front real quick, so it’s 2 inf 2 art on Cauc and 2 arm on Russia, all threatening Ukraine.
If I’m going W. Russia / Belorussia, I’ll usually go 8 inf, or sometimes 1 fighter 1 tank 3 inf. In those situations, Germany can’t really afford to take anything in a forward position anyways. If I get 8 inf, I can make my W. Russia stack bigger earlier. If I get 1 fighter, I can hit Germany’s territories early.