My quest to increase airflow with the fans I have on hand has ended.
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This duct is a smooth spiral around the nozzle with a large enough opening to not stall the fan... I think. The 15-to-45-degree-overhang-test showed great improvement.


Here's the awesome DiiiCooler on the left, with my idiotic 50mm scoop adapter, then my first duct for 50 mm, and then two failed prints of my final 30mm fan duct.
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I'm not sure if I can upload my duct to Thingiverse since The DiiiCooler-license says "no derivatives".