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FEPA 1200 is 7.0 - 2.5 microns at 80%
according to standard 42 D-1984 and DIN 69101
Thats quite a tolerance.
One more factor is the shape of the grain and its density in the matrix.
The...

Well I do not want to rain your parade, but the finer stones are more or less a matter of speculation.
There is almost no possibility to publish something of real evidence about the finer grits....