Is the base tile stack always the same? 46 base tiles, 13 random hazards, 5 random monster?
A few missions (like Hive) alter the setup, but otherwise it remains the same unless you want to change the difficulty or play a short mission (pg. 15)
I see that difficulty is measured by the number of random enemies, and number of hazards... and that the Scout mission is rated as difficulty 2. What does this mean, when the amount of monsters and hazards is the same as in other missions?
Less mathy answer: the more difficult missions require you to do more things, or spend more resources, which makes surviving more difficult. Adding extra enemies or hazards does this too.
More mathy answer: A game with no mission has a set number of resources, and a set number of things that cost resources (enemies.) Since the maximum length of a game is determined by how much food you have, we calculated how many turns you would likely have, which tells you how many total action you can take. We also calculated how many actions it would take you to explore all of the tiles, and keep base stocked during this process. We compared those two numbers to determine the theoretical number of "spare actions" in a game. Each difficulty number represents 10% of those spare actions.
A few examples:
Scout requires you to get back to base, so it uses 20% of the spare actions for everyone to move back to base after everything is explored.
Expand requires you to spend 9 scrap (which indirectly shortens the game since that is less scrap you could trade into food) and build your map in a less efficient way, which together uses 60% of the spare actions.
Changing the difficulty by altering the number of enemies or hazards (outside of what the mission specifies) works in the same way, either by costing extra resources, or costing extra actions.
Keep in mind that the theoretical game that this is based on does not use character traits, so it is still possible to win a game at 10 or higher difficulty.