Ok, then…

My goal was to keep things simple in the first place. It was just a side project, only for fun. So having the Mini untouched was a must, so I could easily get it off, using it elsewhere, or eventually resell it. At first I ran the Mini with its cover off, thinking it would help. It didn't, and the airflow was much better with the cover on

Now what I should certainly do, whenever I find some time to rework on that project, is put a silent fan on the rear panel's vents. Seems like the easiest step, still letting the Mini untouched. But keep in mind that I only rarely use that machine, mainly as an "Apple TV on steroids". But I never watch TV, anyway…