I adjusted the VEFACH (Voron Exhaust Filter Activated Coal + Hepa) vent holes for use with my Nevermore brand carbon pellets. When I measured the pellets they were a little over 4mm in diameter and the length was always greater than that. The vents on both the bottom and top are 3mm x 9mm which is a huge improvement over the tiny vents in the original. No need to play around with infill settings. Just print this and you should be good. I haven't had any issue with Nevermore carbon pellets leaking out of this design.
Note: You'll need to print this HEPA part from the original source if you haven't already.
Credit to KevinAkaSam for the original VEFACH design and for supplying the CAD files which made it possible for me to do this mod.
The author remixed this model.