It’s could be quite subjective as I would prefer the vocal to be at least mid way between the listener and the speaker plane. I understand this would trade off soundstage depth. This leads to another related topic as would you prefer that "they are there" or "you are there."
What you "prefer" then, if you think about it, is a system that imposes your expectations on the music. Every time you impose your desires on a recording you necessarily detract from its fidelity. Think about it.
If you want a good reference for what your system should be doing, try the XLO Test CD, specifically the walk-around tracks. This was recorded in a bare room with two microphones and consists of nothing but Roger Skoff talking and walking around the room hitting a clavis (wood block) while telling you where he is in relation to the microphones.
If your system is dialed in it will be eerily apparent the room is exactly the size it is. The size of your room won’t even matter. Not if your system is good enough. When he says, "I am standing in the middle of the room" so many feet from the microphone you will hear his voice emanating from precisely that location. Then as he walks closer and closer guess what? Like he is right in front of you. He even goes past the microphones to stand behind them. This is the acid test. It is bizarre to hear as it does indeed sound as if he is behind you. In my system anyway.
This is what I’m talking about. Anyone says where something should be, more often than not has no idea. Only using a test CD specifically recorded this way can you have any hope of knowing where things are supposed to image with any specificity. All else is guesswork.