CST STUDIO： Farfield plot's center is not where the port is?

I'm new to CST STUDIO and I'm trying two simulate two antennas together.
What I want to know is when I add excitation to one antenna, how strong would the signal be when it is received by another signal.
The two antennas are both dipole antennas and are designed to be at frequency 2.4GHz and 2.5GHz.
I put one discrete port in one of them and use the transient solver to simulate.
However, I found that the farfield plot is not centered to the port but placed between the two antennas. I consider the result to be wrong. Why is it?