It is widely acknowledged that the mechanical behavior of FRCM composite systems is mainly driven by the stress-transfer mechanisms at the matrix-textile interface. The most applied test setup to investigate the maximum bearing capacity of an FRCM system is the single-lap shear test (SST). Concerning the modeling of results obtained through SST, most works disregard the role of the substrate and mortar stiffnesses, while a few studies consider the deformability of the external or the internal matrix layer. To characterize the different behavior of the internal and external fiber-textile interfaces, two distinct Cohesive Material Laws (CMLs), within a mode II fracture mechanics approach, are considered, and the values are calibrated based on the experimental outcomes on glass fiber reinforced systems coupled to gypsum, lime, and cement matrices. Then, a Finite Difference Method (FDM) model is implemented to interpret the bond characteristics and load-bearing capacity of the tested FRCM systems. The numerical results obtained considering two different CMLs are compared to the ones obtained with a single CML, i.e., considering that the two interfaces have the same behavior.