What also might be happening if you're getting buzz in the higher registers is the geometry is ever so slightly off. Picture a perfectly flat neck/body line and the strings as two long sides of a triangle, with the bridge/saddle height a very short 3rd side. Now, if we put some relief in the neck, one of those long sides won't be straight. It'll start at the point of the triangle, curve away a bit, then come back to the line formed by the neck/body at the point the neck meets the body, and continue straight to bridge. Bit of a transition there.
Now, if you press the other long side toward it, you may go far enough into that dip that the line formed by the string touches the line formed by the neck/body at the point the neck meets the body. In real life, that's either gonna buzz or fret out. Adding more relief to the neck often makes the dip deeper at the same time it's bringing the headstock forward, so the problem may change, but doesn't go away.
If you're still with me, the fix for that is a very thin shim at the headstock side of the neck pocket. We want to tilt the headstock forward just a hair, so there's no way the upper frets can be taller than middle frets. You'll probably also have to take some relief out of the neck to flatten it a smidgen. Net result will be lower action, but you might get into that deadening effect I mentioned.
