Collapsed structures traversed with redshift. Left panel: statistics (mean, standard deviation) describing the average number of subhalos traversed by FRB sightlines out to given redshifts within TNG300-1. Black lines and grey shaded regions describe the total number of subhalos traversed; coloured lines and shaded regions describe the number of subhalos when binned by mass according to the mass bins of Fig. 8. Right panel: statistics (median, interquartile range) describing the average impact parameters between our sightlines and these structures within each snapshot. Overplotted crosses are the impact parameters between observed FRBs and galaxies as calculated by Connor & Ravi (2022), Connor et al. (2020), and Prochaska et al. (2019a).