Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 120)

3 Selecting AI Servo AF Characteristics
120
AF point auto switching
This sets the switching sensitivity of the
AF points as they track the subject
moving dramatically up, down, left, or
right.
This setting takes effect when the AF
area selection mode is set to AF point
expansion (manual selection
), AF
point expansion (manual selection,
surrounding points), Zone AF, Large
Zone AF, or Automatic selection AF.
0
Standard setting for gradual AF point switching.
+2 / +1
Even if the target subject moves dramatically up, down, left, or right
and moves away from the AF point, the camera switches its focus to
neighboring AF points to continue focusing on the subject. The
camera switches to the AF point deemed most likely to focus on the
subject based on the subject’s continual movement, contrast, etc.
Setting +2 makes the camera more prone to switch the AF point
than with +1.
However, with a wide-angle lens having a wide depth of field or if the
subject is too small in the frame, the camera may focus with the
unintended AF point.