  We investigate the structure of the code graph of a multicast network that
has a characteristic shape of an inverted equilateral triangle. We provide a
criterion that determines the validity of a receiver placement within the code
graph, present invariance properties of the determinants corresponding to
receiver placements under symmetries, and provide a complete study of these
networks' receivers and required field sizes up to a network of 4 sources. We
also improve on various definitions related to code graphs.
