In previous works, two mode conversion models, based upon slab approximations, were presented for treating lateral inhomogeneity along the path of propagation in the earth-ionosphere waveguide. One model (termed Full MC in this paper) requires full-wave determination of a biorthogonal set of height gains as well as numerical evaluation of their associated integrals. In the other model (termed Fast MC in this paper) height gain functions are discarded above some height h in the guide and are approximated below height h by Airy functions. No adjoint waveguide is introduced, and the associated integrals are performed analytically. Results of the two models are compared in this paper for air to air transmissions in laterally inhomogeneous environments. Results for both the vertical and transverse electric field are given for source electric dipoles of arbitrary orientation. It is found that the Fast MC model gives excellent agreement with the Full MC results.