Difficulty

From: https://steamcommunity.com/app/1324130/discussions/0/3809530424059945832/#c3809530424061260363
The value we use is called EventProgress, or EP for short. It tracks the following factors in real time: the number of alive survivors, available resources, constructed buildings, and, in certain difficulties and moons, the time elapsed since the start of the scenario.
The EP value varies depending on the selected difficulty level and scenario. In terms of survivors, it's 10 EP per survivor on Easy difficulty, 15 EP on Medium, 25 EP on Hard, 30 EP on Very Hard, and 40 EP on Insane.
Every 10 EP corresponds to 1 minor skarabei in attacks. So, for example, having 10 survivors on Insane difficulty would mean an additional 20 skarabei in attacks. (It's 45 EP for shrierers, so 4-5 Shriekers, etc.)
Regarding turrets, the EP values are as follows: 25 EP for Easy, 37 EP for Medium, 62 EP for Hard, 87 EP for Very Hard, and 150 EP for Insane. (These values are for Concordia, they vary by +-20% between moons.)
Researching technologies does not directly increase the progress. The EP value of new resources produced and buildings constructed helps to balance this aspect.
In most cases, buildings have a slightly higher EP value than the construction resources they consume. However, active defenses such as traps and turrets have an increased EP value.
Each resource carries a different EP value, which is balanced based on the typical amount the player would stockpile. Therefore, excessive production leads to an increased threat level.
If resources are consumed, survivors are killed, or buildings are destroyed, the total EP value of the base immediately decreases. This results in weaker subsequent attacks, allowing time to recover from the damage.