Testing Miller Wavelength Scaling of the Second-Order Nonlinear Coefficients of KNbO{sub 3}, KTiOPO{sub 4}, KTiOAsO{sub 4}, LiNbO{sub 3}, LiIO{sub 3}, B-BaB{sub 2}O{sub 4}, KH{sub 2}OP{sub 4}, and LiB{sub 3}O{sub 5}