FWD offsets are much higher than RWD offsets because a positive scrub radius on the driven wheels is bad news. If you draw an imaginary line through the steering pivot points to the ground, and compare that to the centre line of the tyre, that's the scrub radius. If a FWD car has any scrub radius at all you get nasty self-steer effects as torque is transferred to the wheel - so high offset wheels are used to make the scrub radius zero (or close to it).