Maybe we have a misuderstanding. The value in the AFR-map even in the closed loop area is not part of the fuel calculation. There is no 10% increase in fuel if you change target from 14.5 to 13.1.
That is different from the Delphi ECU where AFR tables are part of the calculation even outside of closed loop.
Yes, that is pretty much it. It is like an on/off switch. The stock O2 sensor is great at 14.5 AFR, but pretty blind to anything outside of it. There it can just read too rich or too lean, but has no idea of how much. If AFR is set to 14.5 and O2 sensor reading is off it will simply start to inject more or less fuel until it has reached the sweet point of 14.5.