Halliday & Matthiessen (1999: 218):
We are now looking at these same circumstantial elements from a complementary standpoint, from the point of view of their own internal composition. As we remarked, a prepositional phrase represents a figure in miniature, with a structure analogous to one component of a figure — closest, perhaps, to Process + Range (so we refer to the participant in the prepositional phrase as a "Minirange"). This means that, shifting our perspective, we can also suggest how the circumstantial elements are related to different figures.