2D histograms of ion speed versus distance to comet surface coloured by counts, with a common x-axis. Top: radial bulk speed of water ions from ICA, in 90 × 40 bins. Bottom: union of the two LAP effective flow speed u_eff, i estimates in 90 × 40 bins and two least-squares regression fits (red solid or dashed line) for two selected intervals, with errors in the coefficients estimated from the least-squares regression.