New to me that 75% of CPU time or processors would limit any project [settings applies to all projects], but cutting in the runtime to run the device cooler (meant for laptops, tablets, smartphones and the like)

Projects parttiming is controlled with the project weight / resource share in the project location profiles (default, home, work, school) and then will work in blocks... for a while WCG, for while Project X, and so on. Hands off, eventually your other projects all get their turn. Manually intervene and the mess will just keep building up... the incomprehension.