Tires are beginning to show "cupped" wear on the inside.

I replaced the tires on this vehicle at 140,000 miles and they showed cupping on the inside of the tread. At the same time, I replaced both front struts with Monroe Quick Struts. After the strut replacement, I had the car aligned. The tires were balance when installed and there is no indication of imbalance now. I recently had the alignment rechecked and a minor toe adjustment brought it back into spec. I keep the tires rotated every 7,500 miles and change direction of the two rear tires when I move them up front. The cupped wear on the new tires is very minor, but I want to solve the problem now to stop it from getting worse.