According to "Reef Aquariums" book by John Tullock, in a Monaco-style system, the false bottom of egg crate is suspended about 1 inch off the bottom of the tank. According to the author, "the Monaco-style aquarium is analogous to the Berlin-style tank in that it relies on natural, bacteriological processes occuring within the aquarium." Dr Jaubert of Monaco uses this approach using the natural properties of the sand to create inexpensive, effective filtration for reef aquariums.
There is supposed to be one or more layers of screening to keep sand from falling through through to the plenum (the area underneath the grid where water, but no sand, is present). Then there is supposed to be 1-2 inches of sand (but not Aragonite). Then another layer of screening is added on the first sand bed and then another few inches of substrate is added.
I am new to salt water aquariums so if this answer doesn't sit well with readers of this website, please don't flame me. I am just reporting what I read in a book so that the person who asked the question can do more research if he/she so pleases. I have no experience whatsoever with this eggcrate stuff and I am neither recommending or criticizing it.