based on this page
https://williamoptics.com/new-adjust...t-not-included
You need to set the ring at 7.9mm which will give you 62.3mm of backfocus to the image plane, plus 0.66 for your filter -> 63mm close enough.
Currently you have 26.5mm so you need to make up 36.5mm with an extension tube or part thereof and the remaining with some other accessory if you want..
Where does it say you need 55mm of backfocus for this reducer?
Personally I only use CCDIn at the moment, but I confirm the results with focus runs in the corners and a visual inspection at 2-400%
Josh