Based on the boundary element method, the frequency-domain dynamic equations of bottom-hinged oscillating wave surge converters under regular and irregular waves in shallow waters were derived. The nonlinear hydrostatic restoring moment and drag moment were linearized as time-independent stiffness and constant damping, respectively. A Python code was developed to efficiently solve the response without significantly sacrificing accuracy. The feasibility of performance enhancement via adjusting Power Take-Off (PTO) parameters was discussed. Under regular waves, the adjusting approaches are classified as no artificial resonance, ideal resonance, and near resonance. The adjustment towards resonance can boost the capturing power, although the flap-type absorber was recognized as a wave torque dominating device. A near-resonance situation, found by scanning the PTO parameters, is more effective to improve the hydrodynamic performance than the ideal resonance, where the amplification of the damping item is disadvantageous. An increasing hysteretic phase angle of velocity relative to wave torque with the increase of wave period represents the best status of wave energy harvesting. Under irregular waves, two adjusting approaches are presented: no artificial resonance and adjusting towards resonance. The performance at short peak periods can be improved by adjusting PTO stiffness, while, adjusting PTO inertia torque is almost ineffective.