In order to encourage smart compositions over simple brute force numerical advantage, I wanted to introduce the idea of a consumable defense that scales by the difference between the defenders and attackers fleets.

I'm going to throw some numbers out here, but none of these are set in stone, just used to give the gist of the idea.

• Minefields will only arm themselves if the attacking force is at a 2x or larger fleet point advantage.
  
• After the first round, if mines were armed and used, they will be destroyed and removed from further rounds. They will not regenerate after battle.
  
• The mines will rapid fire a number of targets attacker_size/defender_size - 1 (so an attacking fleet 2.5 times larger would get struck by mines once, and then each mine having a 50% chance to strike a random target a second time. If the fleet is 10 times bigger, each mine will randomly damage precisely 9 random targets, or the same target 9 times if there's only, say, a single death star and nothing else, but they will also damage targets that are already effectively destroyed or overkilled.)
  
• Mines count towards the size of the defender, so having thousands of minefields and only moderate standard defenses will allow fleets larger than your standard defenses to attack without penalty and without triggering the mines at all, as long as they stay under the threshold point.
  

So with that said, minefields should only be built proportionally with normal defenses, and they only act to deter attacks that would otherwise get away with very few losses, just by sheer force of numbers, rather than thoughtful fleet composition. The formula doesn't even need to be 2x, it could be 3x or 4x or whatever seems most reasonable.

Feel free to add anything or ask questions. If you have a deep grasp of the game mechanics and how things like this would affect the game for better or for worse, please chime in.