Should the firebrick on the edges of the back be mortared to the dome? The instructions don’t mention this but it seems it would add strength plus fill in any gaps.
I put mortar on them and attached them to the dome. It is another way to stop heat loss.
It’s not explicitly in the instructions, but yes, you’d want to do that. I did.
It will look a bit off to your eye, but another example of something you won’t see once you add insulation and stucco.