I find on some guitars I just can't do anything to get rid of the buzz but raise the saddles. This is fine when they happen to set very low but on a few it's just ridiculous. First I adjust the truss rod so there is a small amount of relief seen on my straight edge. This picture is not the best example because I adjusted from too much relief to none and then backed off a bit before snapping this picture but the relief hasn't really appeared yet. I don't have measuring shims but a general rule of thumb I've been following to double check is when I capo the first fret and press down a fret near the truss rod anchor I will be able to easily insert a guitar pick (standard yellow one) between the string and a fret in the middle with little resistance but just enough resistance that it will not fall out if I let it go. But I find tightening or loosening the truss to above and below this zone usually only has a small effect on buzz for better or worse and I often have to resort to raising the saddles. On this particular Strat the action is set quite high but the wound strings buzz pretty much from open to high up on the fretboard. The thin strings are mostly ok and they don't quite choke but don't sustain as much as I feel they should on bent notes high up on the fretboard. I can't detect any noticeable twisting of the fretboard. In this kind of situation where there is buzz all over the fretboard could it just be that one fret like the 18th or something is too high?