Rich vs lean burn.
here are the waveforms, we can clearly see the slight upwards trend in the burn time. That would indicate lean burn or close to it. Yet when tested with aux air there is still enough fuel to push the rpm up by another 300 revolutions. Bringing the burn line to run flat required rich mixture.
Test condition,
Hot engine, high idle 900rpm
Maybe vehicle characteristic, maybe modified ignition coils or oem oversized to give good powerfull lightning strikes, who knows?
If runs fine, let it be, shows we can’t know them all as the book says.