Also found this thread from the F30 forum. http://www.f30post.com/forums/showthread.php?t=687458
Summary of what my finding:
1) Seems like a trend now in the 12-13 model that the exterior mirrors don't dim as much as the older cars did.
2) European models don't seem to have this change
3) It could be due to newer regulation?
4) The exterior mirrors may act on their own and don't act with the interior rear view mirror sensor. They could act from the camera on itself.
5) Dealer may be able to change the coding to change the sensitivity
I will reach out to my SA to find out if there is any way to change this.