I have two different Ryet carbon saddles on my two 268 frames. On one of the saddle the rails measure 9 mm high, on the other 11 mm.
I was asked by Velobuild if I needed a special clamp for carbon rails and was send two sets. They fit fine on the one with 7x9 mm (picture 1) but terrible on the one with 11 mm (picture 2). I just don't think that the side clamping mechanism in general is great on these kind of carbon rails. Should have done my research better before I ordered the Ryet knock off of the Pro Stealth II.
I'm on the look out for a clamp that goes closer to 11 mm than the one I've got.