This paper discusses a study on the optimization of mechanical properties of polypropylene fiber reinforced cementitious material (FRCM) through workability control of fresh properties. To this aim, a simple model is proposed herein describing the contact network between fibers inside FRCMs. The suspension was regarded as a two-phase composite in which fibers were suspended in a viscous cement paste. The theoretical framework presented in this paper and confirmed by experiments shows that there is a critical fiber factor above which the workability properties of fibers are mainly affected by the interactions of fibers in suspension. Moreover, there is a dense fiber factor above which the fibers tend to clump and both workability and mechanical properties of fibers significantly degrade. The obtained results show that adequate workability and a properly adjusted fiber factor are keys to obtain proper flexural and tensile strength. The findings in this paper can provide a rational foundation for mix design of FRCM by adjusting the fiber factor as an effective tool to control the workability of FRCM and practically achieve optimal hardened properties.