What I'm finding, is the edge vector doesn't work well with zone crossing.
My driveway is zone A. The sidewalk, boulevard and road are zone B. I had a 1 pixel gap between A & B, and had zone G covering everything for tracking through the gap. I had 'object crosses zones' set to A-B, so that anything leaving or entering my driveway would trigger. Once I changed the motion sensing to edge vector, it was missing half the motion, even with contrast set to the most sensitive at 12, object size 250 (pretty small), object moves 250, and a make time of 0.3s.
I have now set the object crosses zones to just A. I also increased the make time to 1.0s, and increased object moves to 350. This now causes any directional motion on my entire driveway to trigger. I'll now have to wait for a partly sunny day with fast moving clouds to see what happens, and maybe increase the object moves distance.