True, some 8.5" wheels have lower offsets to deal with clearance issues. This is cheating, IMHO. Look at the big mfgs. (SSR, O.Z./Prodrive, Rota, Speedline, et al) offering wheels specifically for Subaru and you will find offsets of 48-51mm for our cars.
The SSR comps I'm running are 18X8.5" ET48 with 245/40-18 Michelins. They just clear the strut and the rear fender. Moving the wheel out that extra 5mm will better clear brakes and the strut but then the fender and other issues mentioned repeatedly in this thread come into play.
Keep in mind that an 8.5" wheel should get a tire 235 or wider to keep the sidewall in line. Even then the 235 will not protect the lip of the rim. A 245 would be ideal but then with that offset you will surely scrub the rear fenders.
If you really want the lower offset, decrease the wheel width to 8.0" or 7.5". A 235 would be ideal on an 8.0" and OK on a 7.5".
Your choice but there is a huge selection in proper offset for our cars.