Left AF AND focus points problems !
just Tony wrote:
I believe that Thom Hogan's test method calls for the stripes to run horizontally.
Thom is right fopr outer AF points.
The outer detectors a vertically aligned - and there is no detail for AF to detect along a vertical line.
This link from another photographer indicates where detection lines detect on a D600 using single point AF
It is worth while doing a check for each camera you own both in single point Af and also group dynamic where detection lines are much longer.
Nikon change the length and placement of detection lines between camera modls.
Once you know where and how AF sample the image segment you should be able to make more informed AF subject decisions.
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.