This issue comes up ALL the time. Unburned coal in the ash does not necessarily indicate inefficient operation, and perfectly burned ash does not indicated efficient operation. The answer is usually somewhere in between.
Pacowy wrote: allowing cooling air to be blown through the dead ash into the combustion chamber, and reducing the actual efficiency of heat extraction
And there it is...if you are blowing combustion air through dead ash in an attempt to reduce unburned coal in the ash, you are sending more heat up the chimney than would be otherwise lost to the ash can.
Yes the fire and ring are both uniform. No more coal appears to be coming out of one side over the other.
When holding my finger on the tooth pawl, I count 4 clicks as it drags back for the next grab.
Good. I didn't mean to imply that you don't know what you are doing, but you would be surprised how many times folks don't have the feed set to what they think.
Any chance you could post a picture of the fire, ash, and the coal? I am curious how the rice coal is sized.
Lastly, when you evaluate the ash ring it is important that the stoker has been running continuously for at least 30 minutes.