How do I define the lump port of the dipole in HFSS

Hi. I have a question when doing the simulation of dipole in HFSS. It seems the simulation result of half wavelength is quite different from the textbook.
Does the dimension of the rectangle defined for lump port in HFSS affect the simulation result significantly?

for example, I want to simulate the dipole in 900MHZ, I defined the length as 166.67mm, and the lump port dimension is 1 mm height, is it too small? How can i get about 73 ohm resistance???
Thanks in advance