According to one account, on the History Channel, iirc, on his flight from England to Paris on Christmas Eve, 1944, the small plane would passed through an designated "Ordance Displosal Zone" in the English Channel if it had taken a direct route. Planes, other than bombers disposing of ordance, were supposed to avoid these zones. They interviewed one member of a Lancaster crew who were coming back from an aborted raid on Germany. Rather than land with full (or any) bomb loads, they dropped their ordance in these zones before returning to base.
This crew member distinctly remembers seeing a "grasshopper" (small plane) his by his units jettisoned bombs at the time Miller's plane disappeared. The pilot of Miller's plane was relatively inexperienced and like a lot of Army pilots in World War II, had only a minimum of experience. He may have prefered chancing a direct course for Paris to taking a chance on getting lost on a less direct course.
I have heard of reports of a small plane wreck that was seen on the French coast soon after he disappeared but I had never heard of the ODA theory. It makes sense though, I think they would go through all kinds of maneuvers to keep that sort of thing quiet.