Now the cylinder is empty and the propane is gone. As I was checking the machine, I found that the nuts and poles on the back panel were so easy to remove that it gives me a good way to attach the external back panel heater.
Today, I also examined the previous batches and it also turned out that the batches some three weeks ago were more better than the previous probably due to the large quantity of the batches and/or the preheating device. Or, may be the angle of the Leaning Tower of Fuji Royal was too much.
It was really helpful to adjust the rotation to give beans optimum rate of convection heat vs the direct heat transfer from the drum. But it became clear that it is almost must to be able to set the drum rotation and the fan speed independently.