On the Impreza, the wheel offset is noted as "High". Subaru lists High as being between 30 and 55 mm, meaning that the hub contact surface is set more to the street side of the centerline of the wheel. Commonly known as Front Wheel Drive wheels, even though the vehicle may be a Rear Wheel Drive vehicle. That would be similar to the front wheels of the 88 Formula and GT or the Tech wheels of the Grand Am that appear similar to the Fiero 14 inch aluminum wheels.
The 14, 15, 16 and 17 inch wheels are 55mm offset and the 18 inch wheels are 48 mm offset for the 2996u model year.