Results of 1D HD simulations of the evolution of the reverse-to-forward shock radius ratio (R _RS/R _FS) as a function of SNR age for a radially decreasing ambient density profile of the form ﹩\rho =\dot{M}/4\pi {r}^{2}{v}_{w}﹩, where the mass-loss rate ﹩\dot{M}=2\times {10}^{-5}\ {M}_{\odot }\ {\mathrm{yr}}^{-1}﹩ and the wind velocity v _w = 10 km s⁻¹. The curves depict models with the same ambient density profile and explosion energy of 10⁵¹ erg, but with different ejecta masses ranging from 2 to 4 M _⊙. The dotted horizontal and vertical lines represent the R _RS/R _FS and SNR age for G292.0+1.8.