Have you ever seen on an EQ where it says 27K, 36K? Some ridiculous high-end settings and thought, why will I need those, my ears only hear up to 20K. Well, this is how it mix engineers and mastering engineers get really super smooth tops, by adding a shelf at around 32 or whatever that setting is.
The shelf is actually the slope going down. So, the slope that's going down is what gives a really nice, smooth top end. So, by lifting at 32K on a shelf, it's really starting at about 10K, and then bringing itself up to that 32. You're not going to hear the really high stuff, but you'll hear the really nice lush sounding EQ on the slope.