Don't be afraid to mix the challenges a bit...separate the group a bit and get them focused on different things.
I have a submerged group fighting 1
and they're having a hell of a time.
I ambushed them, but poisoned the big hitter(crafter - stupid 10 shift blocks!) before-hand so he wouldn't be around for the ambush (too busy in the bathroom throwing up). He showed up a round or two into the combat.
I compelled the Changeling to leave and go follow someone mid-combat. (the one who poisoned the crafter)
I hit an NPC with a Entropy curse forcing the mage to try to save him.
I compelled the Scion(our prime melee character) to duke it out sans powers because the fight is taking place in public and she can't reveal herself.
She's having a hell of time...although she's getting some really good rolls so she hasn't taken any big hits yet.
It also lets each PC focus on their strengths.
Anyways, I guess the point is to divide the teams focus. Even multiple weak foes is more challenging than one Big Tough Foe. And one Big Foe is probably more likely to hurt people badly in a single hit than multiple weak foes.