It would be better if you made the "funnel" much larger. The more coal you can use to create a "beehive", The better.
When it comes to curing, that's the tough part..... it needs to cure NATURALLY. If you force it to cure, it's going to crack/break, and likely not last more than a couple of firings. That holds true with not only clay, but any type of castable refractory...... the more you force it to cure, the more you shorten it's lifespan.