Interesting, I have the Corsa Extreme on mine and the bed step clears nicely. In fact, the step hit on the factory exhaust resonator, but no clearance issues with the Corsa. I'd say maybe it's the difference between the Sport and Extreme systems, but I believe they are dimensionally identical.
BTW, the way, I didn't notice too big of a difference between the sport system and the stock exhaust. I added the resonator delete to upgrade to the extreme and it definitely helped, but it's not crazy aggressive. If you want obnoxious loud, go Borla or Carven. The Corsa system sounds premium and refined. Smooth as silk I. The highway but step on it and you know you have something. The tone at idle is a nice low rumble with the extreme. You may not hear the difference between stock and the sport system at idle. Also, if you are so inclined, you can save some $$ and have your local muffler shop chop the stock resonator and fill in with pipe. The Corsa resonator delete is just a $200 stainless steel tube.