Predicted 511 keV intensity distributions for the annihilation of ⁴⁴Ti positrons in each transport configuration. From top to bottom, the transport was assumed to be collisionless everywhere (case A, small diffusion coefficient), collisionless in the bulge and ballistic out of it (case B, inhomogeneous case), and ballistic everywhere (case C, large diffusion coefficient). The given intensities correspond to parapositronium annihilation only and were normalised to a positron injection rate of 10⁴³ e⁺/s, with a positronium fraction of 0.95.