All I can add is: “What he said. ^”
There is quite a bit of minutiae that should be considered, but is mostly overlooked. Why? Because up to a certain percentage of volume can be added or subtracted before it really affects the sound quality. So when you are dealing with such minimal differences, that percentage is tiny. That’s why I put that qualifier at the end of my last reply. You should be fine using the 18mm and going more or less straight conversion.
