Photon noise propagation factor (Eq. (6), Sect. 3.4), normalized to the photon count per telescope, as a function of the length of the baseline i, for three array geometries: Y shape (top), circular (middle), and hexagonal (bottom). The fringe tracking baselines are those at unit baseline length. All arrays are inscribed within a circle of radius of 4 (red), 6 (green), or 8 (blue) unit baseline lengths.