I'm convinced this puff-back problem with AHS boilers is really easy to solve. You simply need to ensure there's an open flame to burn volatiles off before they can accumulate. Keeping the fire high enough in the sight tube area resolves this part of the problem; but, due to varying load, weather, etc., it's a pain in the butt to keep changing the PLC "set variable" to keep the fire high in the sight tube area.
Again, the existing AHS design is an open loop control system. Their design really needs to be changed to a closed loop control system; with, a second thermocouple monitoring (and keeping) the fire high in the sight tube area---but not so high you burn up into the storage hopper.
I had puff-backs with my S130---they were simply much smaller.
Gas volatiles occur naturally when when solid fuels transition through their kindling point and combust---this is a completely normal chemical process. No volatiles---no combustion---no heat. It's nonsense to contemplate and compare white ash, red ash, deep mined, strip mined, etc.