You may have your answer already, but thought I'd pass along that my son had the exact same issue with his Eibach upgrade on his 2011 5.0 convertible. The rear ride height was of particular concern. Since many other options looked like we'd have the same problem and we needed a solution, we simply reinstalled the stock rear springs. Left Eibach front springs in. We were concerned on handling, but no noticeable change. I was surprised, but he's also not racing the car. Ride height looks right and scraping and bottoming out pretty much gone. Car is running staggered tire set-up with 255/45/18 front and 285/40/18 rear. Hope this helps.