I just set up my tank this past weekend, 20XT.
Used MGOPM, and some used flourite sand I picked up at an auction.
I sprinkled some dolomite on the very bottom, and then put around 1 1/2 ~2" of MGOPM in, and then another 1 ~ 1 1/2" or so of the flourite on top. the top of the substrate is about 3-4" from the bottom glass, but I've also got a ~1/2" thick piece of slate in there for anchoring the driftwood.
I didn't screen the MGOPM at all, and didn't really notice many pieces much larger then about rice grains or so. I wet it pretty good, and made sure it was pretty well distributed, and then added the flourite sand, and started poking the plants in.
A couple hours (and several beers) later, I finally finished with the planting right about dawn.
I just threw a big filter sponge in there, and poured the (treated) water onto that, and that worked pretty well to keep from disturbing the gravel. by the time the tank was full, there wasn't much cloudiness, and most of it was up in the top, I think from the MGOPM that surfaced during the planting.
So, no real cloudiness with me, but it probably helped that I had previously used (and rinsed) flourite.