I am a little late to the party, but.....If that pic in the first post was full burn, the flames look kinda small to me and there is a wider ash band than I am used to seeing. Anybody else have an opinion on that?
At full burn, I would expect flames at least 12" high and about a 1" band of ash at the end of the grate. But I am used to seeing the flame & ash band on my mag, maybe a koker is different?
If at full burn the flames are not that high on mine I would look for something blocking the combustion air....combustion fan seated properly in mounting bracket, restrictor plate on combustion fan, clogged grate holes, fines built up under the grate, etc.
If the ash band is wider than 1" at full burn then I would look to increase the feed rate a slight bit.
I would only make one change at a time though so you can gauge the effect.