Here's another approach which helps to smooth the level a little:
I place the mic element left of center of the person's head, even a little left of their ear. (No it's not alongside their head; it's still located about a foot in front of them). I then aim the axis of the mic towards the center, but actually so that it's aimed a little in front of the person's mouth. (Of course, you can do the complete opposite and switch left and right.)
When they turn their head to their left, their mouth gets closer to the mic, but it ends up more off-axis, so the net result is little change in level. When they turn their head right, their mouth gets slightly further from the mic, but it's also slightly more on axis, again resulting in little change in level. For best results, you want to use a mic with a fairly consistent frequency response off-axis.
An added benefit to this approach is that, since the mic is not directly in front of their face, it is less vulnerable to plosives. And most of the congregation can see them better.