Well think about it esp with boost the airmass is increased, its travelling at a good rate and has nothing to stop it but the back end of the intake, hits it and bounces off that wall which would induce turbulance bleedback to force it back out the MAF.

It would be interesting to check the flow of the single runners. For example using one of those devices used to check how heads flow.

Is there any official test about that? I bet GM did this kind of measurement during the developement of the LSx intakes.