Hey Robert. I was reading your post and I think the reason that the burner works great out of the forge, and not in it is the hole that you cast needs to follow the 1:12 taper. It looks to me that the wall of the forge is 3 to 4 inches thick. the opening by the time it get to the forge chamber should probably be at least 3 inches maybe more. Im not a math guru but you get the idea. The forge shell you have poured looks nice. I believe if you opened up those holes you would be surprised at the results. I haven't tried my burners at altitude but Im betting they would work great. Also for the forge floor I would get a piece of kiln shelf for that. I use them in mine and they work well. You can insulate under it with kaowool and you wont lose the heat that regular fire brick will suck out.