The formulation of bituminous mixtures has evolved considerably over the last forty years in order to meet the new structural and functional requirements imposed on pavements. In this context, the development of bituminous mixtures has become more difficult and requires precise optimisation both in the choice of components and in their modification according to a grain size curve that complies with the required specifications. Our study aims to examine the effect of bitumen and filler content on the compactness of high modulus asphalt (HMA) class 2. To evaluate the influence of each factor and their interactions on compactness using the Gyratory Shear Compactor (GSC) test, a three-level experimental design was employed. The findings suggest that compactability increases with binder content, albeit to a certain limit. For instance, when bitumen concentration was increased to 6.3%, compactability decreased, which indicated that the mixture was too deformable. The study also indicated that filler materials contribute substantially to the reduction of air voids. These results underscore the necessity of filling to enhance compactability and, thereby, the workability and performance of high-modulus bituminous mixtures. The results, which were further refined by JMP through quadratic modelling, confirmed and quantified the findings by analysis of variance (ANOVA). This analysis illustrates the significance of filler materials in the improvement of compactability while demonstrating the importance of the bitumen-filler mastic in binding the aggregates, thus allowing unhardened asphalt (HMA) to function effectively.