I did the Delferro course and i have to say its a good course. But not all problems start with the diaphragm. With me its my vocal cords. I can control my diaphragm with almost no effort but i have trouble produce words with vowels. It a hit or a miss with the pressure i need to exert on my vocal cords. Which is a technical issue created by psychological stress. For me the program worked due to a feel good effect. But i got right back where i started after i hit a roadblock. For me focusing on emotional and psychological problems has greater effect then a technique that i learned. I do congratulate on your success but what works for one does nothing for another. If it was one solution fits all I had no problem to begin with :)