I did a search to try and find a recent topic i saw regarding mines but typing mines into the seach bar on the forum is not a great idea.

Anyway

Why does the game have to render the mines ingame - those of who you played entenchment early on (was it a beta?) will remember the TEC AI went mines nuts and having loads of mines in a game can really slow it down. Thankfully this has mostly been fixed - mostly

Have minefields as a negative effect - If you build a minefield in a system all enemy ships (different value depending on their size) take damage as long as they are within the gravity well - but you dont need to show them ingame just have it as an negative effect present in the system - mines are removed by conquering/destroying the planet .

This would result in a increase in the game engines performance - i think ...