Sometimes a kiln can have two diameters.
We call this an end bell because normally the feed end has a larger diameter. This can be done for many process reasons, but primarily it is used to reduce air flows in the bell region and in the transfer chute. This description is not to explain all the advantages but to help identify such a kiln characteristic. This picture show 16 to 18’ bell at end of kiln from last tire to preheater.