I just installed a new 105 9sp rear derailleur for use with with my 11-21 cassette. It works and shifts fine, but the b-tension screw appears to have zero effect on the derailleur. After a close inspection, it looks like the metal part that the screw pushes around just is not close enough to the tab it would have to push to bring the derailleur closer up to the cassette. I don't think I really need to move the derailleur closer anyway, but it is puzzling to me. Is this a result of my small cassette? Has anyone had a similar issue? Thanks.