The two-region Okada-Numasawa model for solutions of star-shaped polymers has been improved by means of a change in the integration order and introduction of a concentration-dependent and molar-mass-dependent Flory-Huggins interaction parameter (the second and third approximations of the Flory-Huggins theory). To overcome calculation difficulties, a special algorithm for computing coexistence curves of polymeric systems with an UCST has been used. The agreement between the experimental and calculated coexistence curves for the starshaped polystyrene (PS)-cyclohexane system has been improved: the difference between T(c)s is similar to0.33 K against similar to 12 K as given by the original model.