I'd think an analyst would be able to create a BEM (Boundary Element Model) to predict the difference, without needing to run a CFD for the flow. That's assuming the OTB portion is just an expansion chamber and not part of a long tortuous path. That stated, I collected and processed data for BEM and CFD correlation, but never worked as an analyst running the sims.
Or to think of it another way, the aperture can be used as a flow limiter for OTB (and apparently the Airlock) but not for other non-OTB cans. Why? Really high turbulence (Airlock), or resonator (OTB)? Just thinking/typing out loud.