Nice! I believe that Chuff Sync is still a work in progress. I have the same issues on the three steamers I have updated to use the RP Input wire for a chuff trigger.
It seems that Ring is not using the input exclusively. At certain times, the programmed chuff takes over in order to make smooth speed transitions. That is where it falls flat with extra chuffs when slowing and even when stopped.
I converted a Bachmann Shay a few weeks ago. I don't know if the Shay sound supports the trigger or not. It has the setting, but when using it the chuff is WAY off. After several experiments I went with the voltage controlled chuff which sounds better to me. Unfortunately, the Shay sound really doesn't have a good slow speed sound. It jumps from idle to chuffing fairly fast.