From: Santa Rosa, CA
The key item to up the difficulty is the AI side's Morale rating. From the manual:
Whenever the morale level is set to 110 or greater, then leader admin checks for movement
allowances are always successful (14.1.2) and the Soviet AI is able to build combat units so as
to maintain a force of 300 divisions and 100 brigades at no additional admin cost (see section
12.2.4). In addition, whenever the morale level is set to 125 or greater, all leader initiative
checks for movement allowances points are also automatically successful.
So to give yourself a challenge, you want to set the Soviet morale level to 110. If that's all you do, it will help the Soviet AI tremendously because it will be able to maintain enough units to cover the front. My suggestion would be that if you've played the Road to scenarios and done reasonably well, that you start with everything at 100 except Soviet morale which you can set to 110. If you go with 100% on everything, you will likely win (unless the first winter gets you). You can always change the value, so if you feel you aren't making good progress, at any time you can lower the 110 to 100 and keep going.
All understanding comes after the fact.
-- Soren Kierkegaard