A couple more items to add to what has been said, the feed rate is partially dependent on coal characteristics after all the other factors have been attended to, some coal has less carbon content and therefore takes longer to burn completely resulting in a lower Max value. Also we have used different sized bearings on the Pocono, a 3/4" bearing will have higher max feed rate for the same quality coal than the 7/8" bearing. Coal from the same mine can be different so keeping an eye on what your stove is doing when you attend to the daily routine is always a good idea. Max feed rate is not important, the only real consideration is preventing those little red fellows from jumping into the ash pan before they have given up all their available heat. All stoker motors have slightly different speed and can also contribute to the differences in Max and Min values.
The ash fusing that was described in the original post is also based on coal characteristics, mixing in some buckwheat sized coal will usually solve the issue and help you get a little more heat out of the stove in the colder months.
As has already been stated, proper maintenance of your stove will ensure long and trouble free operation!