One thing I've been thinking that he didn't touch on, is that in-ears are 1) smaller 2) closer to the eardrum. There are fewer paths the sound can take, so it

One thing I've been thinking that he didn't touch on, is that in-ears are 1) smaller 2) closer to the eardrum. There are fewer paths the sound can take, so it should be possible send signals that are more precisely out-of-phase. Another thing I've been thinking about is that the brain uses phase information of sounds to localize sounds. So if ANC changes leaves a small residual signal with a messed up phase, it may be confusing for the brain.