What I was trying to convey, was that when you fill up the diff, whether its the center section of the outside sections, the fill level is the very bottom edge of the fill plug, any excess will just flow out.
BMW made it, so that you can't overfill it. It is the same for the tranny, once the tranny fluid hits a certain level, any excess will flow out. What we did was use an extractor to suck out most of the fluid in the front/rear diff as well and the transfer case.
And we fill it back up until the excess drained out. When it stops, that is when we put the plug in and tightened it done to spec. We did this service back in Nov 2020, and I haven't had any issues. But its your vehicle, do whatever makes you happy.
