It has mostly to do with the wheel offset. The offset measures the distance from the theoretical midpoint of the width of the wheel to the hub. So the closer the hub is to the center of the wheel (lower offset), the more "sucked in" it looks. Wider wheels will enhance the effect as well, at a given offset. Your maximum concave curvature is determined therefore by the distance from fender edge to hub. There aren't really any wheels I've seen for regular 3's that achieve this look, you'd have to stretch your fenders out to widebody status if you want to run lower offsets.
A forum community dedicated to BMW E46, E90, and F30 owners and enthusiasts. Come join the discussion about M performance, turbo kits, engine swaps, builds, modifications, classifieds, troubleshooting, maintenance, and more!