What I find most curious, despite the 1M being a bigger car than the Subaru, is that both keep the same proportion between overall length and wheelbase:
Subaru
4240/2570 (mm) = 1,65
BMW 1M
4380/2660 (mm) = 1,65
So, both have an equally short wheelbase... which in turn means that the tail of both cars will have the same will to step out.
However, the 1M is a significantly taller car than the Subaru... 1420mm against 1285mm. It means that not only you seat significantly lower in the Subaru but also that the center of gravity is again very low and the aerodynamics improved.