Ive always used about 4" of an Ultra Fine crushed coral, aragonite packs up after time IME. Ive found a brand a sand that has great diffusion so there are no truly anaerobic areas. in my coral trays I can put an entire bar of cyclopeeze in for one feeding and absolutely no fluctuations in ammonia,nitrite, or nitrate....not a regular practice but its happened on accident before.
On the other hand, ive never had luck with coarse substrates, shallow sand beds, or BB....maybe I suck.
.02
Sean