Vincent,
I asked something back at the Forge, which you never answered.
Couldn't this "scaling" problem, in theory, be fixed simply be having more monsters?
If three players can fight one standard Storming monster, wouldn't six players be able to fight TWO standard Storming monsters?
That seems like an easy fix, at least for people who have the game and enough dice to give it a whirl. It sounds like you used multiple monsters now and then in your own playtests.
I can see why it might not satisfy your long-term ambitions for the game, but is there some reason that wouldn't work?