While not ideal, an implementation change to stop the afking as a whole group, is to simply have fate completions have a perfect entry chance to trigger the EM.

Long term. This says a lot about SE's game. Your players when enterprise your new dungeon are given the choice of participating in combat, and you know playing the game, or doing nothing and being bored. Choose to be bored. You really designed a winner there. No wonder this game failed once before.