I got the idea the overburn in the corners is not fixed, but harder to notice because of the lower power settings available. If you look at the last picture in @jamesdhatch 's power settings test, it seems the corners are still getting more power than the rest of the square, but that if your material is thick enough and you pick just the right settings you can have the corners not burn all the way through. In his example on baltic birch plywood, 100% power even at the highest speed still shows corner burn-through.
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