Part of the full 3D instrumental response of PAS and VPAS. Panel c) shows the response functions of nine angular bins in the centre of the PAS FoV as contour lines. The respective indices are specified in the legend at the top of the figure. Panels b), and d), give reduced 1D response functions for the same bins. Panel f) completes the 3D instrumental response with the energy response relative to the i^th (E/q)_i step. The blue arrows in panel c) indicate the cut along which the VPAS input angles were scanned for panels a) and e). Panel g) give relative 1D energy responses for neighbouring steps i − 2, i − 1, i, i + 1, i + 2. For VPAS the normalised differential energy responses are interpolated. Panels a), e), and h) show the angles α_z, α_y, and α_x, respectively, over the input angles ϑ_sw, in, φ_sw, in, and γ_sw, in, with solid lines and over the output angles ϑ_sw, out, φ_sw, out, and γ_sw, out with dashed lines. The output angles are derived based on the virtual measurement, whereas the input angles refer to the properties of the simulated solar wind distribution that is measured by VPAS. The dash-dotted lines indicate the respective input angle. Black arrows mark one maximum and one minimum in panels a) and e) and connect to the corresponding 1D response functions in panels b) and d). The shaded grey area in panel c) indicates the scan range used in Fig. 5.