Rotating Glass Holder for Coolscan 9000

[gothambill]

Hello,

I have questions about the masks for the FH-869GR.

I have read the following:
http://www.filmscanner.info/en/NikonSup ... 000ED.html

1) Does the negative rest on the mask, or does the mask go over the negative? I've read on photo.net of a user who believes the latter (he places the negative on the bottom glass, and mask over it).
2) How does one scan film borders, for medium format, or even 35mm - when I tried to scan a single 35mm frame, it was very washed out - the mask I used was far too big for it (any custom masks, make your own mask hints?).
3) There is a small centrally located rectangle on the edge of each mask, I have read (and my 35mm test above indicated) extra light in the scan is bad, should this rectangle be covered by the negative (or something else)?
If I do cover with negative, the scan shape is weird (a weird rectangle with partial image), and the negative no longer fits in the mask (e.g. for 6x6, there is now a slice of exposed glass on the other edge); if I don't cover the rectangle, the scan looks OK - but I wonder if covering the rectangle would have made it better...

4) What is the purpose of that rectangle?
you can see it on the mask here: http://www.filmscanner.info/Bilder/Niko ... buehne.JPG
on the left side

Thanks,
Bill