The numerical modeling of field-assisted ion exchange in glass through a finite aperture is carried out. The effects of unequal ion mobilities and thermal diffusion are included we believe for the first time in the 2-D case. This allows for the modeling of optical channel waveguides with graded index profiles. It is demonstrated that annealing of backdiffused channel guides is far superior to backdiffusion alone in improving their circular symmetry for better coupling to optical fibers.