I'm not a pro, but I have done some shower installation, and it's a subject often talked about on this forum. This is the first time I've heard of this, and I too am skeptical. The method I am familar with is to put down a mortar base. It doesn't have to be absolutely soild, just so the honeycomb is supported in several places. Many of the pros that frequent this forum don't respond to posts on week-ends, so perhaps some of them will give you a more informed answer.