My road bike has a Shimano CS R8000 Ultegra cassette so I purchased the same for my Tacx Neo 2 trainer. However, when the cassette is fitted to the trainer without a spacer, the mech is way out of alignment. When I try a 1mm plain spacer, I can’t get the 11 tooth sprocket on the freehub as there’s none left protruding from the sprocket above. If I tighten the locking ring with the 11 tooth sprocket in place (but not actually on the freehub), my indexing is better, but still a bit out - looks like it would need a slightly wider spacer. Clearly the latter isn’t the right way forward, but what is? Nothing seems to work and I don’t want to have to re-index my gears every time I switch between trainer and wheel. Thanks in advance.