Jim,
You might want to check out the details at this link:
http://birdshot-dgproshop.com/policies/
But, in a nutshell, it looks like BS will run 1-person divisions at a C-tier, and 2-player divisions at B-tiers...just in case you have to stay in MPM division because of your rating.
I generally play in MPG because I'd rather play for cash than more plastic, but I'll move to Am division if there aren't enough in MPG. In your case, I see some pretty good competition in the MM1 division if you are allowed to play in Am divisions.
Larry