Guilin Sun
Ansys Employee

May I know which product you are referring? 

If it is FDTD, it means the result is very senstive to mesh. You will need to do convergence testing and set the override region in the proper location and size and the mesh size. Please do not use coarse mesh to make the simulation volume small. In general we suggest mesh accuracy 2, the default accuracy.

If it is FDE, it may mean that the simulation region   and the mesh are not properly set. 


Anyway 6 order difference is too large to accept. Please elaborate more. You may post some screenshots here.