These engines purely work on VE(Volumetric Efficiency), with zero feedback(AKA Closed loop tuning). In a VE system with zero feedback, every change to the engine's ability to ingest air and expel waste products changes the tuning. Basically, the "VE" coefficient is a guestamate of how good your intake, engine, and exhaust are at flowing air. Any change in the ability to pump air from the inlet to the outlet can't be sensed by the engine, and has to be tuned for. If you make any changes to anything outside of manifold air pressure or manifold air temperature, you need to modify your VE Coeficient to match.
This makes our systems "double dumb" because they not only try to simply approximate the volume of air entering the cylender though the measurement of air pressure and temperature and multiply that by a magic VE coefficient, but they don't have any ability to correct on the back end with AFR readings. In most cars(besides performance turbo cars), I'd call them "double smart" because they both directly measure the air volume with a MAF sensor, AND can correct for AFR on the back end by reading the exhaust. This is why you can throw a pod filter and a rattle can on your honda civic and not blow anything up, but you do that to a YXZ and, like Nate's old posts, end up "Scary lean" with the GYTR tune. The MAF sensor in the civic is directly measuring the volume of air enering the intake, AND if there's any weridness happening, the lambda sensor will catch it on the back end and correct it. Some factory turbo cars(apparently the mozdaspeed3 is one) is actually VE + Lambda, or a "single smart" system. If you have AFRs backing you up, the VE model isn't a problem.
Not to bitch about VE tuning models either, tons of success in the turbo racing world with them. All the guys who aftermarket turbo anything are using VE models now. It's mostly the lack of AFR compensation that's killing us on the Y.