Fit parameters for the 1 au scaled H ionization rate, ﹩{\beta }_{\mathrm{HF}}﹩, and the H ionization cavity, ﹩{\lambda }_{\mathrm{HF}}﹩, derived from minimizing the difference between the SWAP observations and model. The red box indicates the nominal range of 1 au scaled ﹩{\beta }_{{\rm{H}}}(5\mbox{--}10\times {10}^{-7}\,{{\rm{s}}}^{-1}﹩) and λH (3–6 au).