So, the point of the test was to see if it would switch AF points without switching to a different target. Tracking sensitivity is for whether it switches targets or not, so I set it to its lowest setting. I moved the camera around and put closer objects into the frame, and it stayed with the original target. I did not try to obstruct the original target, as it'll eventually switch, just slower than at a higher sensitivity, as I understand it.
got it -- i reread the settings and it makes total sense... i just didnt have my 5d3 in front of me to look