Thanks for sharing the dxf file. I made my diffuser this morning, after tweaking the design dimensions slightly, and it has improved the dust collection more than I had thought it might.
I currently use a Kent CNC dust shoe and before adding the diffuser the downdraft from the DeWalt spindle/router blew chips and dust all over the place (inside the shoe itself), hampering the shop-vac’s ability to such it up. Now it appears that chips and dust head straight toward the suction. Here are a couple of pics and a short video of the diffuser in place. You may just see the chips from the HDPE material heading straight for the suction. Thanks for sharing!
https://discuss-assets.s3.amazonaws.com/original/3X/7/7/771793bac13de15d5540ad8578f995fb0d36825a.mp4