Ratio of the integrated flux density to peak brightness as a function of S/N for sources in the LoTSS-DR1 catalogue. All catalogued sources are shown in red and the sources we used to define an envelope that encompasses 95% of the compact sources are shown in blue (see Sect. 3.1). The impact of varying the limit on the major axis size of LoTSS-DR1 sources is shown with the triangles, crosses, and diagonal crosses corresponding to 10″, 15″, and 20″ limits, respectively. Each of these is fitted with an envelope and the final selected envelope of was derived from the 15″ limit.