feko convergence

hello everyone..
im modeling a rectangular patch antenna with a uslot on an infinite ground plane in FEKO.... however i noticed that the results were different from IE3D for the same geometry. I want to use a coaxial feed but ended up using a wire port in feko.Can anyone tell me if that is the reason im getting the difference in VSWR?i would definitely like some expert advice on this...

i figured how to use the control card to define a coaxial port.but am having convergence problem.Is it because of the segment length? can anyone shed light on this?
Thanks..