All I can tell you is of our method. We place flat brick across the fire pan and draft tubes at the dampers (this supports the other brick courses). The tongue and groove brick is brought up to about 6 inches from the fire door and between 6 inches and a foot from the tube bundle. the side sheet is stepped between them. An old timer claimed that on the finish of job, the top of the brick should be lined with brown glass bottles that are supposed to melt and seal the brick. I tried it once, the glass never stopped flowing and ended as a pool on the fire pan. I suspect that this was a way to justify the presence of the brown bottles.