I've also listened to comparable speakers with those same passages which have a flatter on-off axis response more resembling that of the M22 (based on independent 3rd party measurements) and they do sound more natural in the speech region compared to the M3.

IMO I think it is the midbass-hump that has this affect on certain male voices. Not all, just some. On the other hand it is desirable on some recordings. With the centre speaker though, speech is a primary concern.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne