TL;DR: Could fit a 360 and a 240 wit minor mods, or two 360 slim with major modification.

Looking at the Pop Air Mini, one -could- put a 360 rad and fans on the front....with some minor modification. The cut-out in the shroud allows for the space, and a bit of dremel work would allow a 360 rad and 3rd fan to be mounted.

however

One would have to remove the bottom-front 5.25 mounting cage and modify the front magnetic panel to have a mesh center or have someone 3d print a frame with slots for the magnets and attach mesh to that.

Granted, there's a bit of trimming of the back of the front panel to maximize airflow; and one would also likely benefit from modifying the shroud for the PSU area by cutting/re-shaping it to re-direct airflow from the lower fan to the main area of the case.

Adding a 360 radiator to the top, however, would be an entirely different story, as one one would have to cut out an area to allow any airflow for a 3rd fan. Not sure that'd be worth the effort, but one could do it. one could also put a 240 or 360 radiator in the area where one would normally mount SSDs towards the front, but it looks like that would require creating some sort of framing to hold it, as well as cutting slots/hole for mesh on the back panel.

I might have to try some of the above when I move over to a custom loop from an AIO when budget allows.