When those frets are "low" and buzzing, it means you have too much relief.
Whats happening there is the neck is actually curving upward, so to get a good action, the bridge is lowered. The effect is the part of the neck that is not curving upward - frets 16 to 20 or so will buzz because the bridge is too low.
The remedy - always - is measured... MEASURED setups, until you've done enough by way of measurement, so you can do them in your sleep.
Not knocking anyone... or the poster here... but there is some math involved as to what will actually "work". When folks say, "medium low" action, that is a totally meaningless phrase. When folks say "just a little relief" its equally meaningless.
For the "action", you must remember there are two action adjustments. Bridge and truss rod. If your neck has about .005 relief and the strings are set at 3.5/64th of an inch on the high E and 4/64 on the low E thats about the theoretic limit of what it will do. When you ease the truss rod and the relief moves from .005 to .010 at fret 7 or 8, then at fret 16-17 you've raised the action by .010. Doesn't seem like a lot... you can tell though, since .015 is about 1/64 of an inch, and you can REALL tell that. But, if you let the relief go out to say .015 or .020, then you've got .030 more elevation on the upper frets, without raising the bridge. If you then lower the bridge .030 - a full 32nd of an inch - a huge huge amount.
So, the relief plays a critical, and vital part of the overall string elevation and "action". And newbies and old farts are well to take the measurements... use an eye loup when setting up the guitars, and know the mathematical limit to the action.