Even though you know me as an E.E., I also used to be a professional cabinetmaker for high-end customers. It wasn't just a side-job, it was my sole business.
Anyway, the majority of the time, I would install fixtures toward the front of the cabinet, but vary this as necessary depending on the light cast of the particular fixture.
This Website appears to be for the lights you are choosing, and it even has a diagram for the light cast.
So for this particular fixture, you would want to mount it closer to the rear if you want a portion of the light cast to be on the back wall. (The 7" spacing is for NOT having light cast on the back wall.)
What I would do is power up one fixture and hold it in place under the cabinet and let your wife decide where she wants it located.