I can tell you that on my car (maybe it's an issue specific to second generation models - 02-07, but it might also apply to 08+ models) I don't have an exact even gap all around. It's about one finger, but the gap on the driver's side rear is slightly smaller. The car naturally sits like that, and having a larger aftermarket sway bar doesn't help. My car has been corner balanced and aligned to near-exact specs... it's just the way it is.
I also have a set of BC BRs, so I can't speak for ISCs specifically, but I thought the rest of the info might be helpful.
07 WRX (Albins 5MT + Blouch 20G)
Jorge Carrillo Tuned (365 whp/340 wtq)