Physically the cam tensioners are only capable of two positions, "1" which expands the tensioner. It then presses on the chain and advances intake phase. Position "0" puts cam tensioner into default "retarded" position. AFAIK the ECU has no ability to modulate that into any intermediate phase. It is either, ON or OFF.
In the advanced "1" phase, the intake valve phase overlaps exhaust valve phase by a considerable amount. Normally I believe it is only 2 deg as measured here
http://www.audizine.com/forum/showthread.php/297064-Cam-profile-data-for-all-factory-cams. Add 18 deg of cam advance and suddenly you're overlapping 20 deg, which essentially leaves door open for either exhaust gas to back into intake or intake to exhaust. Due to air inertia though I believe that some clear air pushes exhaust gas out with some fresh air inevitably just escaping through that path. That's the secret behind improved economy and torque on cam advance.
The result though is that engine effectively consumes more air than it is really using for combustion, which would result in AFR inbalance if not corrected via these "helper" tables.
This would also explain notch in MAF readings. Engine is using more air with NWS active than with NWS inactive and when NWS inactivates you see the drop since the venting is not taking place anymore. The engine is using less air now per piston than before.
