I've been doing some illustration for a client's decorative pool they'll be setting in their back yard. It is a product made here in Pueblo by a company I used to be employed as a mould maker with, Haddonstone. At first he had me confused saying that it was a Medium Roman pool, but in seeing that it had only ten pieces had to assume that it was their small Roman Pool. It was presupposed that we could have it done by the 30th of May, in order to provide a nice backdrop for graduation pictures, but if that were so we'd should have been pouring concrete already. I mentioned this.
At any rate here is a side view which shows how much crushed rock and sand there would have to be tamped down (at a minimum of 5-7/8"). I'm not sure how one does such work to that accuracy, including the concrete pad at a minimum of 4-7/8". Somewhere along the line (as the Tech Sheets suggest "work to be done by others"), and knowing concrete labor around here they would just sigh, say nothing and round them both off to both six and five inches.