[zeroryouko]

It depends on the directionality of the mic. Some mics are made to be end-addressed; others are side-address; still others are more or less omnidirectional.

When was the last time anyone saw her singing with a headset mic? She almost *always* seems to use the big, clunky, handheld mic. I don't know that she's *never* used a headset, but I can't think of any examples where she did. Even when she was moving around the stage.

I did some reading up on vocoders after this came up the first time, and according to what I read, the vocals don't so much pass through the vocoder as they are used to modify a signal that the vocoder itself is producing. If that's true, it is conceivable that the input doesn't need to be of very high quality and/or the vocoder might mask the loss of voice volume that would occur if the microphone was suddenly pointed away.