Maybe i should say what i meant ?
I found the part in 4. kind of interesting ,where it talks about inside and outside reluctance of a coil ,the way i understand it by using a coil like we do the reluctance inside is higher ,and so adding ferrite there we get more boost .
Also paragraph 5.3.
Where he says that ferrite rods usually have actually less permeability than stated ?
I am not saying i understand any of his maths ,this paper seems to be made for formula's but ,maybe higher permeability is some thing to be considered .
You guy's have built more of these than i ever will so :P
I'm still learning and thinking (digesting )