Finer point chiselling is visible on the bands on the voussoirs themselves, which were presumably intended to be carved with more intricate decoration.
Although these blocks have clearly moved since they were put in place, the differences in size between the decorative bands of the two middle voussoirs suggest that these were carved on the ground and not in place. While the projection at the top of each block matches up quite neatly, the bands below are carved with different widths.