The current smokescreen is supposed to reduce the target's ability to see what it's hitting - thus the minus to accuracy. It must be pretty thin smoke because the accuracy minus is fairly low.... only -40%.
I'm proposing that high level fire mages get an improved smokescreen.
This smoke screen would create a thick smoke that surrounded just the target's head, thus reducing it's vision at the same time making it less likely that it could dodge attacks. However because the smoke was only obscuring the target's head it wouldn't affect the ability of its enemies to hit it.
In game terms that would me the smoke would put a -70% to accuracy and a +35 to the next attack of any kind, not just the next fire attack. It wouldn't set both a ward and a charm on the target because as soon as the smoke screen charm went away, the trap effect would need to go away as well.
it could be called something like Thick Smoke or something.