Looking at this post here: http://www.flyertalk.com/forum/delta...50-seaters.htm

I'm still questioning myself why MKE-DTW still gets some CR2 flights while there's other flights on aircraft up to 3 to 4 times bigger than one of those seat-filled bear cans on the same exact route. MSN-DTW doesnt get any CR2 flights and MSN is a smaller airport than MKE. And from looking at the schedule on a random date every month there's always a CR9 flight and then a CR2 flight departing about an hour later in the early morning hours. If a CR9 has a 76 seats and a CR2 has 50 seats, that equals 126 combined which is the exact same capacity as an A319. The A319 and the CR9 have the same amount of F seats. And the CR2 and the CR9 combined have about the same amount of prefered or C+ seats on an A319. Just stating some more proof here.