Assigning a port in HFSS

A lumped port is assigned after drawing a rectangle on the antenna feed. How sensitive is it when considering the rectangle overlapping to GND, not in line with the input, small/big by cross section area compared to that of antenna input etc? I am importing the .dxf file of printed antenna pattern, which doesnt match with the grid setting often. Any helpful hints please? Thanks in advance..

maash

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