If you are loading a bisque firing, put the pieces of the same size together for the first firing. You should expose those pieces to at least one section of heating elements in the kiln. If they are not exposed evenly to the rows of heating elements, they might not mature to the same temperature. You can vary their placement. Stack smaller pieces, bottom to bottom or rim to rim. You can also put very tiny, lightweight pieces inside other pieces to save on space.
