MY GUESS:
1. a contract’s difficulty will use the players’ current world map difficulty.
2. renown will affect the world map difficulty.
3. days will affect the world map difficulty.
4. every game you start as new will have its own basic world map difficulty, depends on whether you chose beginner/ veteran/ expert.
5. every game you start as new will have its own basic scaling rate, depends on whether you chose beginner/ veteran/ expert.
i wish the contract difficulty could be scaled depends on how well equiped your men were and how high lvl your men had. or maybe the game is already using this method, just we havent noticed yet?