Tighten it 'till it breaks then back off a quarter turn.
But really, FOG is right far as making them good and tight, especially if you loctite them like from the factory, though I never have. I always use grease/antiseize as it is dissimilar metals to prevent corrosion and I've yet to encounter a loose rotor bolt anywhere, either with one I've worked on or a bike coming to my garage for the first time. They just don't back out.
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