Reciprocal Roof - Opinions on Inner Posts?

I am planning to build a circular house with a reciprocal roof and roundwood.

Current Plan:
- The diameter of the circle is 24 feet.
- 12 posts evenly spaced around this circle.
- 12 main rafters, one over each post join
- 9" thick posts, 9' tall
- 6" thick rafters, about 18-19 feet long. 3' of each rafter is for the eave

In Tony Wrench's book, he adds an inner post under each main rafter (picture from the book attached).

With the above dimensions, is this way overkill, or well worth doing? And what is the best size of this inner circle to take as much of the roof weight as possible? Put another way: At what point along a main rafter should the inner post go?

Hey,
 I have built several recip. Roof structures over the years.Most comparible to your size was "streamsong" in NZ at 22'. Roof rafters were 6" and backed by 2x6 secondary rafters insulated between. Engineered for a living roof. Depends on what the snow load may be!

You leave way too many questions unanswered to venture a decent opinion or suggestion.

~What is your climate, how much snow, wind, rain? What will be the climate stresses on the building? What kind of wood are you using? How strong, how soft, how stiff or "pliable"? Will the wood tend to bend or sag over time? For example, there are big differences between red & white oak, or white and yellow poplar. What are you going to use to hold your upright posts in position, so they don't push out over time? What is your intended roof covering? How heavy? A single layer of tin or canvas weighs considerable less than multiple layers of wood and insulation, or soil and grass. I never have been a big fan of cantilever anything. It can be an attractive building design. But I like things that last a very long time. Putting undue stress on things can cause them to fail sooner than the same well supported materials will last. How you intend to arrange your floor space can affect where posts go.

There are a awful lot of factors to consider when building something you want to remain safe and efficient over time. You need to relate more details for a better estimate.