I thought it was the mirror all this time, but it's not. It's the seat position. For some strange reason, the memory seat position moves down a few millimeters regardless of outdoor/interior temperature. So one day, I reprogrammed seat position 1 where the seat should be and tied a fishing sinker on a string to the bottom of the steering wheel. The bottom of the sinker/weight was set just-so to touch the seating surface of the leather below. Sure enough by the next morning (8 hours later), the seat was about 1/4" lower than the night before. I repeated this experiment three days later ... same result.
2011 E92 335i 6MT (Space Gray/Coral): M-Sport / Premium / Convenience / Navi / L7 / InvisiGuard / Dinan Exhaust & Pedals
2011 CR-Z EX 6MT, 2008 GSX-R600
RETIRED: 2008 Dinan M5 SMG, 2006 330i 6MT, 2006 Dinan 550i 6MT, 1992 Accord EX 5MT