I see what you're proposing, and it could work. But I suspect that if you have burning coals against one side of your tin partition, and unlit coals touching the other side, enough heat could be conducted through the metal to start the unlit coals on the other side. So, you'd have your fire burning from both ends at once. If you leave some space between the partition and the unlit coals, then the fire may burn the way you have planned. It would be interesting to see how this works; if you do it, let us know the results.