It really depends on whether there is any airflow or none. Efficiency of radiators drops with each degree, thus there is significant difference how much heat the heat sink will move. Overall the lower ambient temperature is, the better results are. If you live in hot country then fan which force airflow improves efficiency of overall process. There is significant difference in efficiency of heat sinks between 20C and 35C ambient temperature. Assuming that your computer chips get close to to 100C when they for sure will throttle, you either have delta of 80 or 65C, whereas thermal stuff is not linear, its actually opposite.
Some of Aaeon PCs I’ve seen had a very clever design where CPU was coupled with top of case CNCed in a typical heat sink shape:
If you mounted case bottom to the wall or rail, making radiator part being in front you helped to cause natural airflow and small chimney effect. I saw a lot of mini pcs having “heat sink” style cases, but rarely it is made in above way, making it look nice, but work in fairly limited scope.
Another point - if you have a SSD drive inside computer, it increases temperature of interior and influences thermals. I saw some of catalog cards for Aaeon or another manufcaturer lowering ambient temperature from 65C to 55C just by basic fact of SSD drive being installed inside of the case.