Max I would like to explain a little from what i have found over the past few years , on first light up from filling i always got good gas within a few minutes , but after that i noticed that always lighting was taking longer and longer to get going and also longer get a good quality gas ,it was then when a few of us were talking about how on fresh charcoal they got faster light up times and better gas that i started taking more notice of what was happening to my setup and because my gasifier at the time was a 210 litre drum it was not possible to run it right down and reload with fresh charcoal that in a small unit is easily done .
What i did find out though with a vertical facing nozzle from below on first light up was as i said a very east fast start up and after that longer and longer , it was then i noticed that the reason it was taking longer to light was due to the fact that there was no charcoal anywhere near my nozzle , it had made its own void where nothing seemed to fall onto my nozzle , at least thats how i see it .
Now when i start up i lift the lid and do what the wood guys do , i gently poke a long bar down in the direction of the nozzle and as i get close i suddenly see the level of charcoal drop , i then replace the lid and light from below and it lights up straight away with a strong bright glow and good gas within a few mins .
Nowdays i run my gasifier for roughly 4 weeks@ 4 or 5 hours a week day before i run it down till the gas stops , then the next day i tip it over i remove and slag build up and decide if the nozzle needs replacing or not .
I had also read post from you and others talking about the birdcage and a bell type arrangement to keep the char from the nozzle tip and was myself going to cast a bell type nozzle , until i came across this .