P(z_s|DM_exc) projections after application of Bayes’ theorem for an FRB of DM_exc equal to that of FRB 171020. Subplots consider progenitor scenarios following: (a) distributions neglecting a host galaxy DM component, (b) YPSR distributions in spiral galaxies, (c) homogeneous distributions within galactocentric spheres of radius H = 0.2 kpc in spiral galaxies, (d) elliptical distributions confined to the effective radii (R_e = 3.2 kpc) of elliptical galaxies, and (e) homogeneous distributions within galactocentric spheres of radius H = 0.1 kpc in elliptical galaxies. Uniform (pink lines) and Erlang (grey lines) prior redshift distributions are compared. Vertical lines indicate the conventionally calculated redshift of the FRB. Shaded regions indicate bounds drawn from 68 to 95% confidence intervals. Models are normalised to unity.