<p>The power generation performance of a heaving body wave energy converter (HBWEC) can be enhanced through strategic deployment in proximity to natural or artificial coastal structures. In this study, coastal structures are represented by a partial reflection wall, enabling the device to harness additional reflected wave energy. However, the mechanisms by which the reflection coefficient and the clearance between the wall and the device affect energy conversion performance remain inadequately understood. This study experimentally investigates these effects. The findings demonstrate that the clearance impact on HBWEC power performance near partial reflection walls aligns with standing wave variation characteristics, with optimal positioning near the second antinode of the HBWEC’s heaving natural period. Enhanced reflection coefficients improve energy conversion efficiency within the wave spectrum around the device’s heaving natural period. Additionally, significant water sloshing observed within the clearance may diminish power performance, as verified through computational fluid dynamics (CFD) analysis. This phenomenon results from the multiplicative relationship of leeside clearance with 0.5λ (λ is the wavelength). These insights suggest that practical engineering implementation requires balanced consideration of reflection coefficient, clearance, sloshing phenomenon, and heaving restriction system, rather than individual parameter optimization.</p>