the oem has some kind of ring in the centre where the dv sits on
It HAS to so there so that the rubber ring on the Rev G, or the top of the piston on the DV+ covers the hole and seals against it in order to not leak any boost
Also explains why tuned K04 cars make silly noises on lift off/gearchange - as that hole is never going to flow 300+hp's worth of boost pressure to avoid compressor stall... Well, that coupled with the metre of thin return pipe leading back to the intake