Sorry for the delay in getting back to you on this. Had to move my mom to a skilled nursing facility and it took forever. Everything seems to be slower with COVID.
Anyway, there are a few reasons for the angle. One is response/tone, just the the break angle at the bridge it has an effect at the nut. On a classical guitar there is also a clearance issue with the strings. There is a small range that will work, too far either way and there will be issues.
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