The walls you are referring to must be Bob Barett's or a knock off of his ideas. The guy is a complete nutter (in a good sense), a real missionary, but he's very innovative and, from expereince, knows what he's doing.
For these "boulder walls" its not always easy to make the calculations stack up, especially with respect to strength at the connection with the "facing." The best you can hope to do is figure out what contact area you need to get 100% of the factored design tensile stress (since you'll never get 100% of Tal of the grid, use what's needed not what's available) and specify the contact area in the construction spec.
In summary, its not entirely conventional, but it works and you should be able to figure out a way to make it work on paper as well.
A final word - over 6' and less than 20' is probably okay but I'd start to sweat a bit higher than 20'.
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