Studies regarding renewable energy sources have gained attention over recent years. One example is wave energy converters, which harvest energy from sea waves using different operational principles such as oscillating water columns, oscillating bodies, and overtopping devices. In the present paper, a numerical study is carried out, and a geometrical investigation of a full-scale overtopping device with a coupled structure mounted on the seabed is performed using the Constructal Design method. The main purpose is to investigate the influence of the design over the available power of the device. The areas of the overtopping ramp (Ar) and the trapezoidal seabed structure (At) are the problem constraints. Two degrees of freedom are studied, the ratio between the height and length of the ramp (H3/L3) and the ratio between the upper and lower basis of the trapezoidal obstacle (L1/L2). The device submersion is kept constant (H1 = 3.5 m). The equations of continuity, momentum, and the transport of volume fraction are solved with the Finite Volume Method, while the water–air mixture is treated with the multiphase model Volume of Fluid. Results showed that the ratio H3/L3 presented a higher sensibility than the ratio L1/L2 over the accumulated water in the reservoir. Despite that, the association of a structure coupled to the ramp of an overtopping device improved the performance of the converter by 30% compared to a conventional condition without the structure.