In your case, I don't think the large fender gap has anything to do with your wheel and tire size, especially if you say it seemed to sit high on the stock wheels and tires. If the tire is a smaller diameter, than factory, that could give the larger gap, but that's the only thing I can really think of. Maybe struts but, then again, if they're the right struts for the car it should sit at its normal ride height and, on top of that, your front is sitting on the factory struts. Back in 2007, I had installed KYB AGX's and Eibach lowering springs (Pro-Kit; now discontinued) on my 03 SS.

Thanks for the comments on mine, and yes my 06 has the stock 18's and runs on 235/50R18's (factory tire size).

 

I measured my fender gap in my driveway in front of the garage, but if I pulled out towards the street, the gap became less, about an inch. so maybe it had something to do with the surface my car was sitting on. I guess I'll just have to see how things go after I get the front shocks and lowering springs and go from there. I was gonna get the KYB AGX, but at the time I didn't have the money, and now I can't justify taking off perfectly good, almost brand new shocks and struts and replacing them again. Plus my mechanic might get a little pissed at me lol