Maybe it was in a tip but I must've missed it. At the end of each mission there is a few stats that pop up, the last one is "Average Cover Bonus". What exactly does this % mean?
tl;dr: It's the average amount of defense your units were receiving from cover at the end of each turn.
At the end of each of your turns, the game records how many living soldiers you have, and what type of cover each of your units is in (none, low/half, or standing/full). These are added and stored as
CoverTotal respectively. For
CoverTotal, each type counts as follows:
- No cover - 0
- Low/half cover - 1
- Standing/full cover - 2
At the end of the mission there's a fairly simple calculation:
CoverPercentage = CoverTotal * 20 / CoverCount
This represents the fact that low cover adds 20 defense, and high cover adds 40.
CoverTotal is added to based on the best possible cover for your soldier. Your soldier can be flanked by 6 aliens, but as long as they're standing next to a full cover tile, they're going to count as full cover for the purposes of this calculation.