In a recently proposed model for the injection of steam into an air-filled soil, an equation which defines an unknown coefficient in terms of the parameters in the model arises. The paper examines this equation. It is shown that the coefficient is well-defined. Furthermore, quantitative and qualitative properties of the dependence of the coefficient on the parameters in the model are derived. A crucial role in the analysis is played by the Mills ratio for the normal probability distribution. By the bye, bounds for the Mills ratio, which to the best of the authors' knowledge are new, are obtained.