So both DL 181 and DL 1131 from LGA to DTW are flown on A319s. Yet DL 181 is coded as having Business class while DL 1131 has "First" class. It took me awhile to realize why my "low" reward was clocking in a 200k miles (LGA-DTW-HKG). Anyone able to explain how two different flights on the same airplane one has J and one has F?