A long time ago, in many galaxies far, far away (sorry, I just couldn't resist)...
I used to play a game called SpaceMerchant, which was based on the old TradeWars 2002 BBS game. The way that game eventually implemented mines could, IMHO, be adapted to SEIV.
SpaceMerchant had a map system of usually many "galaxies", each galaxy a square of sectors that wrapped; think a system map in SEIV, where if you were in the top right corner, and moved right, you'd be in the top left corner. However, you couldn't always move between adjacent sectors, there were paths that had to be used. Galaxies were linked via warps.
So, for each sector, there is a maximum of five entrances/exits. The way SpaceMerchant did mines, the total number in the sector were divided by the number of entrances, and a random modifier was applied. When you moved into a sector, that amount of mines would "attack" you, and a certain percentage would blow up next to you. The effect was: you got a small amount of damage (usually not enough to come close to killing you, unless you were already close anyway), any course you had plotted is erased, you lose three turns in the attack (turns were often very limited, 1 move = -1 turn), you're decloaked.
From there, you had a few options. If you went back from where you came from, nothing else happens (unless some mean person laid mines there while you were in the other sector
). If you continue attacking the mines, you face all of them at once (there was a max of 50 in a sector). If you try going through some other exit, you don't move, and it's the same as if you just entered the sector, but, the sector you tried to move to is now the "safe" sector, where you can go without worrying about any other mines in the current sector.
There is a bit more to the mine stuff in that game, but I don't want to explain the entire game, and that gives a general idea of how they work.
That could be modified for SEIV. When ships enter a minefield, 25% have a
chance of hitting, and an extra movement point is taken. If the ships withdraw the same way they came, they don't encounter any more mines. A sweeper can stay in the field and attempt to sweep the mines, having a
chance of getting all, or none, or anything in between. If ships attempt to exit some other way, 25% of the remaining mines have a
chance of hitting, an extra movement point is taken, and they can continue. Ships cloaking are turned off on encountering a minefield (they'll know where you are from the pretty explosions, after all).
Change the sweeper's rating's from "Can sweep X mines" to "Can sweep X warheads", and have them destroyed on use. Moddable, of course, for those who would like their mines to be more/less powerful.