back in 2018, during fires, when air filters were unobtanium, on bayarea subreddits (and probably here) were floating a lot of posts of DIY filter made from box fan + hvac filters. plenty of people also posted particulate count reduction charts.

you don't need a lab to figure out that replacing 1" filter with 4" filter and even better arranging multiple filters in a box will improve flow rates and filtration (especially for box fans that not really designed for static pressure)

corsi&rosental work, imho, is equivalent to lab work reporting that you can move more water through 10" pipe than through 1" pipe.

I can see that argument, but I think what they contributed was that there's something approaching a cost-optimal design. they reported that the 4-sided design with box fan had higher CADR than many if not all commercially available filters though it often used more power and was louder, so the filtration per dollar was very good