I think staying at one perfect distance from a condenser is probably bad technique, unless the singer has *no* dynamics, which I have never heard. The pickup pattern(s) of a condenser mic and its proximity effect is quite variable. You move relative to a condenser mic quite a bit. Guess what? I find it's very cool to *be somewhere else when you breath!*. Some songs and mics call for "swallowing " the mic and being wicked close to it. Others want to be backed off say, 8-18", but it's different on every song. Some mics just do or don't work for a singer on a specific song. The mic that just sucked could be great on another song. Ain't life a bitch?
Tell your singer that you move in and out on a cardioid condenser to control output and proximity, just like a dynamic mic, but like the difference between a truck and a sports car, little movements with the condenser produce big results. Your singer needs to learn what this mic is all about, and it takes time and practice. She must learn to play that mic, like a new guitar. It's an instrument, not a point and shoot camera, that just captures the sound you make. -Richie