alt Hacker Newsi did think the 4-sided design using the cardboard box as a base was very efficient. one of the contributions here was Corsi and Rosenthal did this in a lab and reported particulate counts, flow rates, and energy usage. So there was some kind of intellectual contribution to broaden adoption by giving it more of an imprimatur of quality
other refinements were using a shroud to prevent back flow
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.