I just took some measurements and I am really unsure of my suggestions now. My boa is 6 and 1/2 inches around (and it had just fed), and it is eating medium sized rats. The "medium rats" I've been getting are about 5 and 1/2 inches around. If you're boa is really 11 inches around, it really should be getting more than a medium sized rats or that equivalent in mice.

I'd suggest measuring with string of some sort wrapping it around the fattest part of it and marking it with a permanent marker then measuring it when it's straightened out. On the pictures in your other thread it doesn't really look VERY big, but the pictures might be misleading.

Good luck.