There is tons of info on this subject but I have yet found, still looking for you, any info on sediment size for denitrit, that is "best".
There is lost here, to help you undestand;
http://www.ozestuaries.org/indicator...efficiency.jsp
There is also the book the book I mentioned;
Introduction to the Study of the Meiofauna
which abounds with info but nothing on denitrif..
IMHO, based on data and articles, it makes not difference what the sediment size is, in research or in nature, just whether or not it is taking place. You only need a hypoxic zone. It should be obvious, that it can occur in any sediment size and maybe that is why it is not an issue in research papers or books. What you are trying to do is a little different, create a hypoxic zone, based on sediment size, in a reef tank.
Two of my books really get into the subject of bacterial biogeochemistry ( the actual title of one), with chapters just on sediments and denitrif. and neither even breaths the word sediment size. All of the articles I looked at do not either.