TE, you have found out what a couple of us have been screaming for quite a while. On these little smokers, a clay saucer robs you of heat and fuel. With space at a premium, the more fuel used to heat the clay saucer, the shorter your burn times will be. I simply foil the steamer tray, and that has become my diffuser. By not having the clay saucer absorbing heat, you achieve the desired temp faster, and can maintain that temp longer. It's my opinion that the clay saucer acts more as a heat sink then a diffuser. I really like your build, and your "Tin Man" heat shield is nothing short of genius!
Great Work,
Tim