Neck relief is an easy check. Capo the first fret and hold down on the last fret of a strat. Check and see the space between the string and the 8th fret. If there's no space, you need to loosen the truss rod. If there is too much space, you need to tighten.
Generally, fret buzz up around the 9th-15th frets will be caused by too much relief. Fret buzz on the lower frets would be not enough relief. There's not really a need to eye ball anything, unless you are eye balling if the neck is twisted or something. I don't measure neck relief. I put enough relief in the neck that the strings don't buzz. It doesn't really matter how much that actually is,
Again, neck relief is something you should always be checking before setting saddle height. I literally put the order down in an earlier post.
If that doesn't fix it, then you are down to buying a straight edge and grinding frets, which is something I've never had to do.