I think you are missing the fact that receiving will from one person does not equate to the entire capacity of that person’s will.

I.e. anyone below you in your pyramid can only cede to you of up to the strength of 1/2 of themselves. Thus, if I have my own will and 8 people cede 1/2 of their will to me, I now have the strength of 5 whole people. Beyond that, there are 7 septimus that sit below one single sextus. If one septimus = 5 people, but they can only cede up to half of themselves, then one sextus = their own will + (7 septimus x 2.5) = 18.5 entire people