Please don't take this the wrong way, but that's a really bad idea, if what you're trying to do is thicken a vocal track. The slightest head movements will cause major phasing problems and drastic level changes.
The only time (all of this is in my opinion, of course) it makes sense to use two mics on a single vocal is if the song goes from really soft vocal levels to screaming. You would set one mic for the soft levels, one for screaming levels, then switch back and forth at the appropriate times during mixdown.
You're better off putting down two separate passes on the vocals, use a whisper track, or add some chorusing and delay if you want to fatten the vocals up.
But, you might as well try it since it will only cost you a little time. If it doesn't work, you've learned something, and who knows - it may create an interesting effect, and that brings up a whole new subject - what to do with mistakes.
Always think "outside the box" when listening to everything. Let's say using two mics on the vocal sounds really weird when you play it back. Don't just throw it out. Stop and think, "Hmmm, would that sound good on just the verses? Or maybe just on the chorus?".
Sometimes a strange effect may not work on a whole song, but it may be perfect for one verse, one line, or maybe even just one single word in the whole song.
I guess I'm saying that, yes, it's a bad idea, but it may have interesting results for other reasons, so it makes sense to try it, and then learn from it.
If it doesn't work, file that sound away in your head (and how you got it) for future use someday.
BTW, when you have about a million of these "fuckups" stored in your brain, congratulations, you're now a professional recording engineer.
