The lower the profile of the tire, the lower the car has to sit to "look right", so the lower profiles in the rear make it look as if it is sitting higher. Personally I like the tire right at the fender lip, no gap, that way it doesn't look slammed but still low.
I would love to lower mine a little more, but I scrape the bumper as it is pulling out of my driveway, and with the offsets on the rims I have I rub on hard bumps. After a little more work on my set up (mainly rolling the fenders)and once I move to a new place, she will go down further. (one of the beauties of coilovers :icon_bigg ).