The 2011 rear springs are definitely different from the 2009s that my car came with. The shape of the 2011 springs is uniform top to bottom. My 2009 M sport spirngs were not. They are slightly smaller at each end than in the middle.
2009 BMW LeMans Blue 135i/Dinan Stage 2 software upgrade/Alufelgen SF-71s/M3 suspension pieces/Koni Sport adjustable dampers/ETS FMIC