The design of the 89-91 E30s came with a lower rear-wheel arch. Try looking for pictures of a 1990 and a 1987 E30 and compare the rear arches and you'll see what I'm talking about. It gives the appearance of a sagging rear.
When people lower there car, it compounds the sagging butt look, so a few companies (such as Vogtland) make lowering springs with rake; ie, front -1.7" rear -1.3" as on my car. This way it evens out the fender gaps, with the inclusive aggressive rake look.