Contour plot corresponding to a column-normalized 2D histogram of the SWE helium abundance as a function of the proton speed observed at Wind. The solid green line and error bars are the mean and standard deviation in each column. The dash-dotted pink line shows the result of a bilinear fit to the green line, where each line is selected as the minimum of both lines in the bilinear function over the full domain. Only speeds of v_sw > 300 kms¹ are included in the fit. Semitransparent blue lines indicate the saturation speed (v_s) and saturation abundance (A_s) along with their uncertainties, where the bilinear function changes slope.