I seem to remember a thread from some time ago which stated there is some difference in the glass, or curvature, or "something" related to HUD. I don't have time to search just now...
Bimmerfest Supporting Member
2011 535i AT | Black Sapphire/Cinnamon | Premium | Heated Sts | Nav | Sirius | Anthracite Hdr & Trim
Prior: 2008 335i 6MT Sedan | Black Sapphire/Terra Leather | Premium | Cold | CA | OEM Alarm
Prior: 2005 330i 6MT | Black Sapphire/Sand Leather | Premium | Cold | UGO | OEM Alarm