Air to fuel ratio changes will change
exhaust gas temperature which changes
the speed of sound in the exhaust gas
which will change the rpm at which the drone resonance will be loudest.

I had not thought of it before but pumping in cooler outside air into a hot exhaust system would change the rpm at which drone occurs. If a 12V air compressor was used it could be switched on/off to observe the effect. In a low backpressure exhaust system a forward facing "draft tube" might add enough air to shift the drone rpm.

We have discussed T junction stubs to cancel drone here on moparts.
The Flowmaster resonators in the post above have a stub of pipe inside the resonator case. It looks neater but you cannot "fine tune" the effect by lengthening or shortening the stub length.