Guilin Sun
Ansys Employee

This is a genius yet approximate method, the same as the metalens. In metalens, the elements are simulated as infinitely periodic but in the metalens they are not. However their combination indeed functions as a lens. Plese read this section: Nearfield stitching and farfield projection. This method tries to save simulation time, in particular for very large dimension.

As you can see, when stiching the near fields, they are not continuous.

As for the overlap and edge weighting, I guess it is a kind of compensation. You can try to not overlap and see if the result can be better or worse.