Preferential surface texturing is expected to significantly improve tribological performance of ultralow flying magnetic storage head-disk interfaces (HDIs) by modifying the roughness and reducing the contact area preferentially, thereby reducing the relevant interfacial forces, such as friction, contact, and adhesive forces. Because of the different etch rates in the titanium carbide (top surface) and alumina (bottom surface) portions of the slider air-bearing surface (ABS), during reactive ion etching the surface heights possess a distinct bimodal distribution. In order to accurately and realistically capture the interfacial phenomena of the ultralow flying HDI with a preferentially textured slider ABS, a probability density function was proposed by linking two different Gaussian asperity distributions. The proposed bimodal asperity distribution was then directly incorporated into a previously developed rough surface contact model to calculate the corresponding interfacial forces. The results were then directly compared to a single Gaussian approximation (ignoring the bimodality) as well as a high-order polynomial curve-fit approximation (encompassing the bimodality). Comparative studies revealed that the proposed bimodal distribution method has a main advantage of being able to resolve the top and bottom asperity contributions separately, which is physically more accurate, and thereby providing interfacial force estimates that are more physically accurate. Other simpler methods, by assuming a single continuous distribution over the entire surface, are not able to isolate the top and bottom asperity distributions and thus are more likely to overestimate the interfacial forces in sub-5 nm flying HDIs.