As the temperature increases, more and more of the heat is transferred by radiation from the heating elements. For uniform heating, it is important that all surfaces of the ware be exposed to heating elements. At low temperatures, heat moves primarily by convection. This is not a very efficient method. The hot gases and some radiation heat the surface of the ware, where it is conducted into the ware.
Sufficient time is needed to move heat to and into the ware.
Unless we move the heat through the kiln by mechanical means, the hot air will naturally rise to near the top of the kiln and the cool air will fall to near the bottom. We may see up to a 2 cone difference from top to bottom in the kiln at low cone values. Soaking or holding the kiln at temperature can help equalize heat, but truly uniform conditions will not naturally occur until higher temperatures, where radiation is more effective. Even Heating Ware Heat moves through ware from the outside to the inside. It is important to try to uniformly heat all the surfaces of the ware.