Voice goes off at the direction where your character is facing not where he is looking. I don't think you can turn away from a locked target as far as I know, I've never used lock target for this specific reason. I would recommend playing without locked target, since as a caster whenever you cast a spell if you have auto face target on, your character will turn and face the target anyways. Kiting the Renauld while having your target locked on him is also a bad idea since you won't be able to run as fast, this will severely hinder your ability to kite properly and setting the Renuald at an ideal location. This may also cause you to fire off voices at a undesirable direction while kiting petrifying your raid.