Maybe the '05 Boxster doesn't have height-adjusting collars on the Boxster either. The 911s had a metal ring (collar) at each spring. When turned, they raised or lowered the corner for corner balancing. When we got the car about as well balanced as we could, the fender lips would usually be at different heights side to side. Mine were usually about .5" different, but I've seen some with greater differences.

My guess is that you should look further into that much side-to-side difference.