Canon EOS-1DX MARK II Settings Manual page 72

Auto selection AF is effective to include the
background (on the right or left) in the photo
Hints & Tips
With AF4 [Initial AF pt for AI Servo AF during
Auto selection AF], it is possible to have
Auto selection AF start from a manually
selected AF point.
During AI Servo AF, if the [Initial AF pt for AI Servo
AF during Auto selection AF] setting is [Auto], the
first subject to be captured will be selected
automatically — usually, the nearest subject.
When you want to start shooting from a manually
selected AF point, set the initial AF point to a
setting other than [Auto]. (Refer to P. 121)
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