Not sure this will help the OP but here goes.....I read over this particularly good thread: https://www.dootalk....=air fuel ratio
But I did not see one thing discussed that has an impact on the AFR readings from an O2 sensor in the exhaust with a 2 strokes in particular.
Anytime that there is unburned fuel passing from the intake to the exhaust, an O2 sensor is going to read lean. This happens for 4 strokes when warming up, and with huge cams that give a lumpy idle. It happens for 2 strokes when warming up AND when you are hard on the throttle and the scavenging is carrying some of the intake fuel-air mix out the exhaust.
The reason is this: An AFR gauge that uses an O2 sensor only measures the % of free oxygen in the exhaust, and interprets that as AFR in the intake. When full combustion of the ingested fuel-air mix is going on, then the free oxygen content in the exhaust is an accurate reflection of the fuel-air ratio in the intake. But when some of the intake fuel is not burned, then the oxygen that goes with that unburned fuel is also not burned, and that unburned oxygen shows up in the exhaust as free oxygen. This excess free oxygen in the exhaust is interpreted by the AFR gauge as a lean condition in the intake fuel-air-mixture.
So I would not expect an O2 sensor-based AFR gauge to give accurate readings under heavy loads, big throttle openings, and higher RPM's on a 2 stroke. (And actually, this has been known for a long time...) I would expect the readings to be lean (high). It will read accurately at low to mild throttle and RPM, and idle after the engine is warmed up. The seemingly high AF reading posted by spookum in post #25 of the above linked thread is very probably explained by this matter.
So the only use for an O2-sensor-based AFR gauge for the OP under hard throttle conditions is to see if there are sudden and very large spikes upwards in the AFR readings. The typical readings at hard throttle won't be accurate. (EGT sensors for 2 strokes are used for a reason.....)
And detonation can be caused by other things than air-fuel ratio. Excessively high head temps is one good cause.