middle null object expression?>

[Walter Soyka]

You just need the average of the two points. Something like this will work as an expression on the position property of a null layer (modify layer/tracker names as necessary to suit your comp):

p1 = thisComp.layer("TRACK_LAYER").motionTracker("Tracker 1")("Track Point 1").attachPoint;
p2 = thisComp.layer("TRACK_LAYER").motionTracker("Tracker 1")("Track Point 2").attachPoint;

(p1+p2)/2

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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