Re: Sorry to ask again but...
I see two primary advantages of fluid mounting. One is the elimination of Newton rings, which can be a problems with some films (TMAX-100 for example) even when scanning emulsion down on glass. Another is an increase in micro-contrast. It is the increase in micro-contrast that appears to give more apparent sharpness.
Thanks for all the info Sandy, which makes a lot of sense...But now I wonder, if the focus is so good (as with the tintype, etc.) why the oil? Is that only about Newton rings? If so, honestly, that poof with cornstarch is a piece of (so to speak) cake.