Thanks for getting back to me.

As I said, it doesn't matter how full the respective disks are (and if I ever manage a stack where they all really hit 87.21% at the same time, I'll try my luck at Powerball for sure).

They're from entirely different manufacturers, and their usage is wildly different. Mind you, it does show real numbers when I open the RMM fly-out, just not on the summary page. Funnily enough, CPU and MEM usage are presented differently there, as they should be.