another extract from the same microgen page referring to dutch john's design and guidance... "...With your large diameter lower housing forcing the nozzle tips so far out from the walls you are going to have to now add a tar fence underneath the nozzles so the engine gumming tar vapors cannot sneak/bypass behind the hot, hot converting planear burn zone just in front of the nozzles. With this as it is built so far you are also going to find you need to build up an internal slope cone from where the fuel hopper feeds in to just above the nozzles ends. This could hang down from your upper/lower housing seam line. You can read this described and line drawn pictured, and the why of it, in Dutch John's MicroGasifier article. This feed slope needs to be ~60 degree from a vertical plain to the nozzles then imagine this 60 degree line carried on past through the nozzles tips to the outside edge of the lower hearth reduction hole. Hearth reduction hole need to be sized based on the expected fuel gases flow rate as determined by the engine, the fuel type, and its chunked size...."