These PCMs and tunes are way way smarter than you think. They are watching and reacting to the weather conditions, water and oil temp, recent drive history, catalyst temps, knock sensors, etc...

It's not picking that AF on accident.

For what it's worth I work at Chrysler and had a lot of 1 on 1 time with the calibrators in my scat pack (392).

They don't need a wide band to know what the engine is doing in the NA range.

Just because the PCM isn't showing you the AF number you expect, doesn't mean it wasn't intentional.