Tung has constructed a sum-rule-constrained classical binary-collision model for the estimation of generalized oscillator strengths (GOSs) of the 1s and 2s subshells of atoms. He applied three sum rules to determine the momentum-dependent parameters introduced in the GOS function based on the classical binary-collision model. Several deficiencies have then been found regarding these sum rules that adopted the less accurate hydrogenic model and included the unwanted contribution from discrete excitations. In the present work, we have reconstructed this model by employing improved sum rules obtained from Hartree-Fock-Slater matrix element calculations. The refined model has been successfully applied to estimate ionization generalized oscillator strengths of atomic K and L shells.