Dependence on the distance from the HP (HP1 definition) of the average angular distance |Δ_θ| between the simulated perpendicularity condition and the observed IBEX ribbon for different LISM magnetic field strengths, shown in panel a. Panel b: how the minimum of each profile in panel a depends on the LISM magnetic field strength. Colors of circles in panel b correspond to colors of lines in panel a. The minimum of the simulated dependence shown in panel b gives an estimate of the LISM magnetic field strength that provides the best fit to IBEX ribbon observations.