The present study attempts to improve the results of the well-known quasi-chemical (pair) approximation for systems with short-range interactions. Using an analogy between expressions arising in information theory and in statistical thermodynamics, the procedure of derivation of configurational factors for 2D Ising models was found which guarantees nonnegative sign of the configurational entropy at any set of point and pair probabilities. The present approximation predicts values of critical parameters for 2D Ising models of a ferromagnetic with the accuracy of 1-3% in comparison to the exact results for square, honeycomb, and triangular lattices.