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On the N54 at least, the MAP sensors are just in front of the throttle body and also in the intake manifold........
Therefore further downstream than the air filter and subject to lots of oil contamination from the crankcase vapours.
Besides, if you watched those videos I linked carefully, you would have noticed the comments about OEM's placing charcoal filters in the air box as a pollution control mechanism due to residual vapours migrating backwards into the intake system once the engine is shut down and making their way into the atmosphere via the the air filter/MAF sensor housing.
MAF contamination is not as simple and straightforward as you think it is.
It's always easy to blame the oiled air filters, but those videos show some compelling evidence that speaks otherwise and they base their conclusions on empirical testing.
Hope you caught that bit about a burn off cycle on the thermistor at start up to help burn off contaminants from the MAF.
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