Duratrans or Fujitrans in cut sheet

How is your film arrangements, or setup when you are creating mask?
Like do you use an acrylic sheet above the glass, emulsion up / down?
I’m at the beginning of my journey, and following tips and tricks as much as I can. With BW negatives, I guess I’m there with Ortho Lith film, can develop it without any issue and fix it as well. Yes it gets brown, but very uniform, max du is around 0.2 with low contrast.
For C41 films I follow up your advise on FP4, correct filtration etc.
Overall I’m still gauging on how much blur I need so your setup might give me more ideas.

It would not be practical to outline all my masking methods here. I don't personally use acrylic spacers, but know certain people who have. It tends to create just too much unsharp halo for my own preferences. I most often use 7-mil frosted mylar instead. There are many variations involved, depending on whether a single mask is involved or additional steps potentially involving multiple masks.

I have quite a bit of specialized punch and register equipment, and which gear is specifically being used also determines the film orientation itself. For simple jobs using a registered masking contact frame, the original film would be registered onto the anti-newton glass emulsion up, then with the 70mil mylar sheet positioned between that and the masking film itself, which would have its own emulsion placed down. I'm referring to sheet placement on the work counter, before the contact frame is closed and flipped over for sake of actual exposure on the enlarger baseboard itself.

@DREW WILEY could you please give us a link of your frosted mylar? I have found few examples but they are all glossy and translucent. Not really matte so will create newton rings.

I buy all of mine locally at a big art store, which is now part of the Dick Blick chain. They also have website ordering, with a large selection of this kind of product. The 5-mil product is much more resistant to handling than the 3-mil version. Look under the following : Grafix Dura-Lar Matte (two sided matte, frosted on both sides) or Grafix Drafting Film. You can choose anywhere between packs of 9X12 inch cut sheet up to very large rolls.

In either case, inspect each sheet, whether pre-cut or cut by yourself, over a light box. If there are any blemishes or inconsistencies in a particular sheet, don't use that one for an untextured portion of a scene, like an open sky. I sort out my own cut sheets into "grade A" (completely blemish free), "grade B" (only minor blemishes in a portion of the sheet),
and "Grade C", which must be used with caution. Most of it amounts to Grade B; so I reserve the completely blemish free
Grade A sheets for very fussy applications.

And again, I'm referring to frosted mylar, which Dura-Lar specifically is. Frosted Acetate is also available, but is not dimensionally stable for long-term registration purposes, and has a much more apparent frosting pattern which might reproduce in portions of the print.