Select which face to check for "Center to eye"

The centre to face and centre to eye features on the Focus window have been fantastic for shots with a single person. But with multiple people in frame, the feature is hopeless for selecting the dominant face, and will often even select an out of focus partially obscured person looking mostly away from camera.

I'd love to choose which face is used and then have the software focus on those eyes going forward while we shoot. At the moment it keeps snapping back to the wrong person with each new frame, completely removing the utility of the feature.