I've tried lowering the SV to lower the degree of partially burned coal in the warmer months, and I've seen little benefit from this exercise. In my opinion it's most likely the coal. I was in the same boat this season until it got colder here. Last season I saw no problems during the warm months, as UAE Harmony burned clean to ash even in the summer.
The partially burned coal situation will improve greatly (and will likely go away completely) once you start getting T-Stat heat calls on a more routine basis. But even with the presence of partially burned coal, the AHS is highly efficient. When you compare the coal burned daily over the summer for an AHS, it is mainstream normal with respect to the reports for all of the other boiler types out there. For me the summer difference was about 13.5 to 14 lbs. burned per day for the UAE (with no unburned), and about 15.5 to 16 lbs. per day for Blaschak (with plenty of visible and weighable partially burned stuff).