Upstream speed, u, multiplied by the average density, N_p, of the sheath+LE as well as the magnetic structure. The solid lines give the linear and fourth-order polynomial fit, respectively. For comparison, the dashed line gives the empirical Leblanc solar wind density formula (Leblanc et al. 1998) for a 1 au density of 9 cm⁻³, multiplied by the average upstream solar wind speed as derived for our data sample (∼375 km s⁻¹).