Did you try blowing air through the mass from bottom up? It can help loosen the grass chips, reduce moisture and prevent agglomeration and is useful as long as the air flux doesn't prevent the grass from funneling down.
Certainly we considered it. The problem is that on this prototype system we were operating with a sealed hopper. Thus any gas injected into the hopper would travel through the system and dilute our output gas stream. Also any oxygen in the injected gas would result in combustion rather than gasification.
The inside of the funnel can be lined with a tube punchered uniformly and use pneumatic nitrogen piped from above and outside of the sealed hopper? I’m getting these weird ideas in my head.