I'm in the process of creating an enclosure for my prusa i3 mk2 and I've gone the lack table way that seem to be popular. I've been looking at all the different filament guides, they seem to be mostly small holes or long narrow holes. Both make sense.
I'm going to be bringing my internal height of the enclosure up to 18" with the addition of printed parts that double for holding the acrylic sides in place. I've been told that the small hole would be a detriment to taller prints so the long hole would work better. This is where my idea came in, with the wider cone base that goes on the underside and the small hole at the top the pivot point of the filament is raised an additional 1.5" which should be enough with the extra height of the enclosure to allow for a small hole right at the top. At least that's my theory, still to be tested. I wanted the small hole to keep the ABS vapors in the box as much as possible.
I designed the bottom for a 2.5" hole (cause I have a hole saw bit that size). It should screw into the bottom, then the top piece should just fit inside the bottom piece from above, some glue if you want (I didn't).
My approach seems to have worked, I just screwed up the dimensions on the hole size (modeling newb mistake) for the larger cone. It 'fit' but I obviously need to downsize the cone, i'm betting by the thickness of the cone walls.
Updated the files with better dimensions now. Outside of the cone is 2.5", so a hole saw of that size will work well.
This is no longer untested. I have run several prints through and moved the filament full left and right at full height, works well. Note: my enclosure height (bottom of the cone) is at 18" exactly, as this is the precut height of the acrylic that I purchased and designed my risers around.
Paired with my filament spool holders I feel like I've got a well working system in place