This paper addresses the problem of evaluating the accuracy of a ray-optical solution for the corner diffraction coefficient, which was recently derived by Albertsen. A spectral domain approach is employed to test the satisfaction of the boundary condition on an acoustically soft plate scatterer as a measure for the accuracy of the solution. The results of the test show that the corner diffraction coefficient requires improvement, and an iterative method, also based on the spectral domain approach, is employed to obtain refinements of the original solution proposed by Albertsen.