There's a different finned cover for the non-M cars, comes on Z4 and auto ZHPs.I just did a quick lookup and found this from Bimmerworld
Fits all non-M E46s, required for limited slip diffs! The E46 Finned Differential Cover installs on all E46 323, 325, 328, and 330 differential housings. If you have a custom limited-slip differential, you need this diff cover to protect your investment!
No I do not have an e46 Me but a 330i and a 323i
As you can see the mounting to the subframe is very different, but what's more difficult to see is that the differential case is larger on the M so that cover cannot mount to the non-M diff housing either.