D5100 focus and recompose

I was trying to get a full body shot with the 85mm 1.8G, I used single point AF pointing at the model's eye, then recompose so I can see her legs in the frame. I took several shots, all of them do not sharp focus on thte eyes, it's a little soft on the face overall.

I was not using the center focus point, just one of the edge AF points. The focal point was moved from eye area to about shoulder area. It didn't move that much, but seems to be affecting the focus. I was using f5.6 and 160/s, with SB910 and SB700.

Generally I can still get sharp focus, but it's not always 100%. Is there a trick using the shutter half way focus lock and recompose?