ads momentum ground port

hi,

ADS momentum assumes an infinite substrate and ground plane. however, in real world antenna designs, the ground needs to be truncated like for example in a dipole array.
Im designing a dipole array for a WLAN base station.
I use FR4 board with a strip metal layer above and a truncated ground plane below and some vias.
I have used "ground reference" port, that is i have a "single" port for my feedline and another port for the finite ground below.
I tried different settings but they have suspicious and different responses like placing the ground reference port along the edge, inside the truncated plane and then using internal port at the feedline.
But still i got different results and im anxious about the validity of my design.

My question is :

what is the correct procedure in simulating a dipole array antenna with a finite ground plane below and a single port(internal/single) at the feedline above using ADS momemtum (ADS2005a) ?

Thanks in advance!
blue...