I noticed the same issue this season (this is my 4th season), I burn oak, maple, ash, apple and American cherry, all burn hot if dry. I find that oak will produce 1400 degf reaction chamber temp and burn 1/4 cord to a fine dust that won't fill a 5 gal bucket.
I found that my water temperature sensor was reading 20 deg less than what the boiler reads. I checked the wiring from the controller to the sensor and all connections in between which all checked ok. After replacing the sensor the temp difference reduced to 15 deg.
I was running the boiler set point @ 185 with a 10 deg difference, with a twenty deg difference to actual water temperature I was barely making thermostatic valve temp at the low end.
I increased my set point to 195 ( max) and now I find that the boiler is burning the coals to dust, for the most part but I still have an issue with the temp sensor which I will take up with my dealer.
I would suggest checking the temperature of your water leaving the boiler and compare to what the boiler reads. Let me know if you have questions, I'm curious to learn what you find.