[GuidoK]

Look for rufford ford clips on youtube. They're famous.
BMW's do seem to score not so good when imitating a submarine....
Lots of clips of people totalling their car (waterlocked), and BMW's seem to suffer maybe more...

Then again, when confronted with such high standing water...maybe look for a different route.
All those peoples in those clips (and in those dodgy chinese links) are TOTAL IDIOTS....

Like already said, the air inlet on bmw's is usually pretty low, behind the kidney's, about in the middle hightwise.
The air inlet is pretty low because the front of the car is pretty low on bmw's platforms. The i6 (and i4 too) is slanted, so placed under an angle. Therefore the engine sits lower (lower gravity).
Lots of other cars have a platform that accomodates an upright inline engine, and have an air inlet almost at the top of their grille.