Keep it three feet from the wall and four feet from the floor. If the singer is left handed keep him three feet from the door on his right side. If the singer leans on the wall, put him on the floor.
Keep the NTK 12" from the singers mouth and 3" above his mouth(angling down at it but don't let him sing "up" into it, he sings straight ahead and use a pop screen filter. This will tame the sibilance a bit and when you eq you may want to roll off a little 12k or so