I don't know about your camera, but on my Nikon's, auto focus is driven by the exposure mode the camera is in.
- In "Auto" the AF is set to "closest subject." So the camera will focus on anything that is close, thinking THAT is the subject. I stopped using auto after one try. I had chairs, tables, dinner plates, etc, etc, in focus, but my subjects further back on the other side of the table was OUT of focus.
- I now use P, so that I can select where I want the camera to focus on.
In Canon's area focusing, the manual says similar, "closest subject."
On my old D70, I locked the camera to center point AF. This was because it was difficult to see the AF point that the camera would select. It did not light up bright enough to be easily seen, and I regularly missed which AF point the camera selected.
I am also forgetful, so if I moved the AF point away from the center, I was/am likely to forget and leave it there, messing up my next shot. I have an excuse for this, old age
Derrel has an interesting point. I noticed on some of my shots, which I "thought" were out of focus, it really was in focus. When I zoomed in on the face, I could clearly see the eye lashes, and they were IN focus.
In my case, I think the issues is, that the clothes are bright and have more visual attraction than the small eyes and eye lashes, so by attracting the eye to the clothes, it visually looks like the clothes is in the focus point.
Note to self: Tell subjects to NOT wear BRIGHT clothes to a portrait type shoot.