Digital BW, The Print

Hello group...Hope someone can help me with this.  I am scaning using
the SS120 and PolaColor Insight for my 6x7 work.  (I also have
SilverFast, but it won't work with the glass film strip holder for
6x7.)  I want to scan in greyscale for a variety of reasons.  When the
preview screen is set "B&W negative" and I then try to go to either
the curves screen or the histogram screen to set the black and white
points, my file size triples.  I suspect by setting the black and
white points the software is scaning in RGB.  I don't know for sure,
because the file size keeps bugging up the PC and I have yet to open
one of these monsterous files to see if it actually is RGB.  If I
don't set the black and white points, I get the expected greyscale
scan with the much lower file size.

Am I doing something wrong here?  Can't I set the black and white
points and still get a greyscale scan?

Any help would be appreciated.

Val Brunell