Characteristic impedance of CPW

Hi,
There are two solution type in HFSS,including driven terminal, modal based. I want to simulate the characteristic impedance of CPW. The simulation report contains port Zo and Terminal port Zo in modal based and driven terminal, respectively. The simulation results of the two solution type is deferent with arond 3 Ohm discrepancy. I wonder which solution type I should use as I wanna know the characteristic impedance of CPW. Thank your kind response.:D