on the 2013, they call it the 'Structural reinforcement panel' and it's part number
31106786568
The bolt is:
33306772888
The stiffening plate on the 2013 model does not also share the bolts with the sway bar which is good, it uses the same diameter bolts just shorter, so i have a strong suspicion that BMW will have spec'd the same rules for install but maybe with different values since it's a shorter bolt (35 v 55 mm).
I haven't found the directive yet but in the link above it should show.