The whole thing seems a bit off to me. Adapters vary in equality, and fit.
At the same time is every sensor, from a given camera maker, equipped with the same thickness and quality of glass in the stack?
Did Nikon and Canon lock themselves into a set filter thickness/composition for all time and eternity?
It would be interesting to know if filter stack thickness has changed as sensors have evolved?
Then again, what about emulsion thickness? Which is optimal?
Or, are the differences too small to matter?