Cyanobacteria/Dirt bottom connection? help.

I read in a post that if you allow your MTS (mud) to extend all the way to the glass instead of bordering it around the perimeter with sand or your cap material you will encourage BGA (Cyano.B.) to grow there. If the post is correct then perhaps Cyano likes mud, or mud and light together... I do see Cyano where my mud touches the glass and my fine play sand cap is about an inch deep on average but quite thin in places due to the goldfish sifting it. I used a thin cap because I have a very fine sand as a cap and wanted to allow some nutrient to percolate down into the soil to replenish it. Perhaps I should have used a deeper cap, or a larger grained cap. Anyone have any experience with thin fine caps? How about suggestions? Should I add more play sand? should I add a larger grained sand such as pool filter sand on top? I plan keep all of my other factors static then disturb the mud and see if it indeed produces a Cyano bloom (several times) to test the theory. So far two blooms have followed disturbing the substrate.