I don't know why it would improve a situation by rotating the sensor. Not enough info. I will guess that Banks encountered some turbulence not otherwise persent, and it may present the MAF to the thrust of the turbulence. The MAF design is directional. It could be that the position that makes the problem occur may be too high a volume, and turning it could reduce the perceived volume. Goes back to what I said the first time. I could tell you what the EGR is supposed to do, but can't tell you why it does what it does when it doesn't do what it's supposed to do.

A Diesel engine can't run lean. It can be too rich (excess fuel it can't burn completely), but that's the black smoke that gets expelled. Lean a Diesel, and it slows down. There is no "mixture". There is no controlled restriction in the intake to control the air, other than the later models, but that's for the EGR and DPF, not mixture. #2 does not require the 15:1 like gas. It's variable according to the fuel properties (which varies from kerosene to bunker oil), available heat, injection and combustion chamber design.

Your last statement sounds like you are getting closer to understanding. At the same time, the PCM tracks the air volume trend as well as the given known volume values.

All that said, the engine will run fine with the MAF disconnected. It will be sluggish off idle and lack power, but will still run near normal. Try it. The SES will show up and you'll get a MAF code, but it will still run and respond to pedal input.