If the endurance is 8 hrs, and it can only fly 125 km, that’s only 15 km/h or about 9 mph ground speed? Even if the 125 is out and back range, that’s only 18 mph? The 125 limit has to be something to do with control range as you say.
It has a top speed of 126MPH so speed * time = distance which would be ~1008 miles. Speed source here:
http://www.military.com/equipment/rq-7b-shadow
Controlable distance is 125 km, 8 hrs. flight time doesn't mean in a straight line. They do back and forth scans of territory......