I have a Suntour Cyclone MKII RD, which supposedly is able to handle up to 32T on my Vitus. It was working well with a no-name 7 speed freewheel with (I think) 28T as the biggest, and a KMC Z-chain, and Campy friction shifter.
As an experiment I tried a 6 speed Shimano "corn-cob", which only goes up to 20T. Strangely, I can't get it to shift onto the 20T, and I'm out of adjustment! This does not make sense to me since I know it can handle the range. What am I missing?