Longest sequence optimising the MST on averaging distance from all frequency bins. The sequence includes 21% of the original set, shown in Fig. 4. The symmetry constraint (Sect. 2.4) implies that neighbouring profiles in the sequence can be considered similar when inverted in phase. All sources that are mirrored with respect to the root pulsar J0614+2229 are marked with an asterisk before their name, and we display inverted profiles at all frequencies. We note that the apparent shifts in the 400−700 MHz bin between the J0437−4715 and J2145−0750 profile are not, by themselves, a cause for concern, as the profiles displayed here have no underlying intrinsic physical alignment (in contrast to, e.g., a multi-frequency plot). Regardless, the black colouring of the warp between these two profiles indicates a relatively large distance.