Hi Chris
I find that my Mewlon 210 is quite sensitive to having the correct Back Focus with my Tak x0.8 Reducer / Flattener (from 8-10 years ago). My R/F has a 2" Push Fit into the telescope end and a 54mm Female Thread at the camera end.
Not sure if the current model Tak x0.8 R/F has been updated in the meantime though?
Also, I think it is a Reducer / Flattener rather than a Corrector, as I end up with slightly comatic stars at the edge of the field.
Here is my set up as an example.
Cheers
Dennis