Ross, thanks for the detailed explanation. It makes sense to me now. You're right, I misunderstood your point.
I have the same adapter you mentioned - the adjustable one. I wanted to use it with my ASI071 which has 17.5mm sensor distance as well. I was able to set the adapter length to 30mm, and including my 3mm thick filter inside, the effective length was 46.5mm. I was able to focus to infinity without any problems. But I did have bad tilting issue, so I stopped using it.
Is the adapter cause tilting issue?
we sold hundreds of this adapter and it must can reach focus with Nikon lens