Breakwater-integrated caisson-type overtopping wave energy converters (OWECs) can retrofit port infrastructure with energy recovery, and their performance is strongly influenced by submerged-ramp geometry that governs underwater wave-particle motion, reflection, recirculation, and localized breaking. This study establishes a depth-selection framework based on the cumulative distribution of wave-induced kinetic energy from linear wave theory and applies weakly compressible smoothed particle hydrodynamics (WCSPH) simulations using DualSPHysics under regular waves to quantify how hydraulic efficiency responds to ramp slope and installation depth for single-slope designs. Guided by these trends, a segmented multi-angle ramp is proposed to preserve the upper-slope function required for overtopping while reducing submerged volume and foundation demand. Performance is assessed by combining hydraulic efficiency with construction-quantity-based economy indices. Results show that deeper ramps generally enhance efficiency but with diminishing returns, and that the preferred slope depends on the installation depth. In suitable depth ranges, segmented ramps provide a practical compromise between material savings and retained performance. The proposed procedure supports early-stage geometry screening and robust depth-range selection across site conditions.