Somebody should inform this guy too: http://www.icmag.com/ic/showpost.php?p=1981935&postcount=11
I see my plant's roots fill the inside edge of the container very heavily too.
But on the inside it's mostly coco. I had another plant exactly like the one shown, but I kept this one to reveg. I cut a lot off the root ball and then put it back into the same size container. A few weeks into flower I transplanted it into a container twice the size it was in. When I dug her up, I saw that her roots really had not penetrated the new coco much at all. Interesting...