This photograph, taken by Reaktion Books publisher Michael Leaman in Tiblisi, Georgia, very clearly shows that the top of the oven is angled so that breads stuck to its side will receive direct radiant heat from the embers or fire at the bottom of the oven. If you build a tandoor oven I would use this photograph as a model.
This video offers an introduction to baking bread in sand heated by a fire of brushwood. This particular version is made by a Berber but it is a technique that is widespread in desert regions. The YouTube videos documenting the method tend not to offer much information on the dough and how one version might differ from another. It seems to be a process that limits baking to one bread at a time. If any of you know whether a second bread can be baked in the same hot sand and embers, please leave a comment. I haven’t tested this method.