Syndrome of "Man in mask"+ stupidity of the heroes. Again (SPOILER!)

[Shougun]

I replayed my own voicemail once and could've sworn it was my brother. That's exactly what my brother sounds like on the phone when i talk to him. Neither of our parents nor his wife can tell us apart on the phone.

Our own voice sounding different is not quite the same as other people, we hear our own voices through our head - so that experience isn't really comparable to listening to others. I can recognize most actors by their voice, I'm awful with faces - so I'm not sure how much voice tone would change my judgment on who is who but I could say that a mask muffles/shifts stuff so that's possible.