Simulated density profile along Voyager 1 and 2 trajectories for the case where B_∞ = 0.3 nT. Locations of three HP definitions are shown in the plot: HP1 (based on the maximum slope of the density profile), HP2 (isocontour n_p = n_p∞) and separatrix-based definition HP SEP. The inset shows in detail the region embraced by dashed lines in the main plot. The main plot uses the logarithmic vertical scale, while in the inset, the vertical scale is linear.