A flatwise glued laminated timber–concrete floor system can be connected with dovetail-type notches. According to EN 1995, its design requires metallic fasteners. Splitting occurs in such connections, leading to complex stress states in timber, combining tension perpendicular to the grain and shear. Timber failure is strongly influenced by material heterogeneity, including knots and their associated grain deviation. These features motivate conservative design rules, which only partially capture load redistribution and geometric effects in complex timber systems. Damage models therefore provide a relevant framework for analysing crack initiation, propagation and load redistribution in heterogeneous wood substrates. This work focuses on analysing the mechanical performance of the timber notch. A numerical approach investigates the system effect in flatwise glued laminated maritime pine under localised loading representative of timber–concrete dovetail connections. The FE modelling relies on an energetically regularised damage model for wood, accounting for its quasi-brittle behaviour in the three material directions. Material defects, such as knots and grain deviation, are implemented. The model, derived from previous work and experimentally validated, is implemented within a finite element framework. The numerical study considers lamellas with known material singularities and highlights marked differences in the mechanical behaviour of individual lamellas governed by material heterogeneity. When lamellas with pronounced singularities are glued together, the global strength increases significantly. The simulations highlight the central role of the system effect by providing explicit insight into the progressive development of damage zones driven by the quality of each lamella in the composite material. Mixing lamellas with low mechanical performance with better ones leads to a global response approaching the strength of defect-free wood. This numerical work thus supports less conservative design approaches.