This paper recalls the combined hydrodynamic-aerodynamic scaling requirements for small scale physical model testing of OWCs due to air compressibility. General considerations and an analysis of test results indicate complications associated with the implementation of these requirements. Through numerical simulation in the frequency domain it is shown that the disregard of the requirements leads to considerable errors in the prediction of the prototype behaviour from scale model tests. This is dependent on the absolute size of the representative air chamber height at full scale. A perturbation expansion method is employed to quantify the non-linearities associated with the simultaneous changes of interior air pressure and air volume. These are shown to be of significance at full scale but not replicated during small scale physical model testing when the established scaling requirements are applied. An alternative method is proposed where the fixed additional volume is replaced by a significantly smaller variable additional volume at model scale. The variations of this air volume may be controlled passively or actively to substitute the required air compression and possibly other effects that influence the hydrodynamic-aerodynamic coupling in accordance with the full scale conditions.