Is the low limit screw all the way out (or in, I forget which)? In other words, is it possible that the 11 is just marginally too far to the right for the RD/hanger combination? I had that problem with a Red 10-speed RD on a Giant TCR Advanced frame. I had to shim the RD out slightly to the right of the hanger with a washer. Worked perfectly. Plenty of low limit screw adjustability on the other side to be able to get the largest cog even with the shim.

BTW that will also put a little more tension into the RD spring when shifting to the smallest cog in case, as said above, that is what is needed.