RULE OF THUMB I JUST DISCOVERED: If a typical encounter is one that has a 50% chance of producing a mild or moderate consequence, it looks like ...
1.) a single FAE character is equal to an opponent with +3 offense/+3 defense and four 1-point stress boxes, with a mild consequence slot or a +2 combat stunt. (It really matters who wins initiative.)
2.) a single FAE character can handle TWO opponents with +2 offense/+2 defense and two 1-point stress boxes (again, with a mild consequence slot or a +2 combat stunt)
3.) a single FAE character can handle FOUR opponents with +1 offense/+1 defense and a single stress box. And possibly a stunt so they have a chance in hell of hitting at all, though they do get four tries.
This further suggests that two players can handle a +4/+4 opponent with six stress boxes, and four of them can take on a +5/+5 with eight stress boxes.
So that's my new rough model going forward: +3/+3 ()()()() as the baseline, and drop a number or raise a number every time you double the combatants on one of the sides.