Grid of mass loss rate modelling for VX Sgr, U Her, RR Aql, and W Hya. The contours represent the base-10 logarithm of the reduced -value from the fitting of CO lines. The horizontal axis describes the mass loss rate variation and along the vertical axis the CO photo-dissociation radius (R_1∕2) is varied. The black dots indicate the grid values and the white cross indicates the best fit values. The solid line represents the CO photo-dissociation radius vs. mass loss dependence as predicted by Mamon et al. (1988).