1. A method comprising: obtaining acoustic cement evaluation data points deriving from one or more acoustic downhole tools used in a wellbore having a casing; processing the acoustic cement evaluation data points using a solid-liquid-gas model to assign at least some of the acoustic cement evaluation data points to a material of solid, liquid, or gas in an annulus of the wellbore behind the casing, wherein the solid-liquid-gas model comprises: a tight solid-liquid-gas model in which a gas threshold range is not directly adjacent to a liquid threshold range; or a solid-liquid-gas model that considers flexural attenuation only when a pulse-echo-derived acoustic impedance is below an evanescence point; or both.