I cut these five blanks on my fretboard jig a long time ago. Now I finally want one, so I pulled one out at random, and it turned out to be the worst of the batch. By worst, I mean it was thin in the middle and thick at the ends, probably because it is not perfectly flat and and sat on the jig with a slight bow that I didn't notice.
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There are two components to intonation. The first is simple - locating the bridge at the right spot. You'd think that would be obvious, you'd be surprised how often it is gotten wrong. Like my Rickenbacker. The second part is the additional length or 'compensation' needed for each string beyond the scale length. That derives from the string's mechanical resistance to bending, or its stiffness, which is proportional to its diameter. That's why the low fat strings need more compensation than the thinner ones - shortening the string increases its relative stiffness, or the ratio of diameter to length, and causes it to go sharp as you go up the neck. I have never seen a negative compensation, I think theoretically it should not exist.
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