Hard to say. If a trimmed small flat, I might want to know where my Smokette is the hottest, and put it there, and crank it all the way so it is not sitting in low heat all day drying out like jerky, then I would foil at about 150*. If a big full packer with lots of fat, I might want it low and slow for a good while, then crank up after the plateau, no foil.
It's gonna take alot of experimentation to get brisket down pat.