The "attenuation volume" issue is precisely why the SIR sits way out on the front of the airbox, where we have seen it in F3, FIA sportscars, etc. - or so I've read. Remember that air is a fluid - it flows and eddies and stuff. I can see how it might confuse things, putting the SIR close enough in front of the MAF that it in essence creates a blast of increasing-velocity air from that little hole.

Particularly if I didn't have a bottomless engineering budget, I'd be tempted to build the biggest airbox possible, and use the SIR as the inlet. Put the filter between the SIR and airflow sensor, to leave things as much like the OE MAF is used to seeing them, absent the restriction, and count on the flexibility built into the system to cope with some of the variables that remain, short of sonic velocities being reached at the SIR.

K