[Captain Kwok]

Here is another way mines could work:

The chances for a mine to hit a ship could be a simple chance formula where the maximum mines that can be in a sector represents a 100% hit chance for ships passing through. Each mine laid counts as a % of that total. For example with a 100 mine limit, if you had 20 mines that'd be 20% to hit chance for each ship passing through. So, say 50 ships were passing through in that example without minesweepers, perhaps 10 ships would take damage or be destroyed.