4mm , 120 film and its papers movement GAP in DIY 6X16 Camera

My aluminum 6x16 Camera Design is waiting its que to be laser cut at industrial center. Its only a box with two internal walls which protects the film rolls from internal light and have 4mm gap for film + paper movement .
Is that 4mm gap too much or not enough. ?
I found felt and velvet are suitable materials to close that gap to light leak and prevent film scratch

I am only voicing my thoughts on this and I am by no means an authority on fabrication or camera building. 4mm sounds like a lot. I cannot think of a method to accurately measure the space inside a normally functioning camera.
One idea I had a while back would be to scavenge the pressure plate out of an old folding camera like an Ansco speedex or something like that (cheap, not sought after folding camera that used 120 film)
I think some combination of felt/velvet should get you through a testing phase at least and may work long-term.

Do you have drawings, sections, or such to show what you mean by 'gap'? I can't picture what you are talking about.