Well, in the case of a headset it's a non-issue either way as we won't be using it, so it's not really better or worse either way. As for using it by the ear or via speakerphone, if you were to move away to look up something and moved your finger a bit around the edges of the screen there's the potential to hangup with a large wide button vs. a smaller centered one that would need a more deliberate action. As far as what it looks like and how aesthetically pleasing that's certainly something in the eye of the beholder and can't really satisfy everyone of course, but as far as usability/experience, there might just be something to it being better somewhat smaller than somewhat larger when a wide range of users and everything else is considered. That said, it is what it is (for whatever reason).
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Realistically it's only inverted in comparison to what it was before, otherwise, taken on its own, it's just fine and works the same.