This paper describes an EoS/GE approach based on cubic equations of state making reference to low pressure GE models derived from the lattice fluid theory of Guggenheim. The proposed method does not present the theoretical problems encountered with the literature reference states (infinite pressure of Huron-Vidal, zero pressure of Michelsen and constant packing fraction of Péneloux), namely the description of the alpha function with combinatorial terms derived from both the excess Gibbs energy model and the EoS. The main advantage of the proposed method is to successfully account for the size-asymmetry of mixture components and to improve the results obtained with the Wong-Sandler mixing rule. Comparisons are performed with the MHV1, LCVM and the original Wong-Sandler approach at infinite pressure.