Confirming S parameter reference plane

In reading the comments for the RX LNA S parameter files I wanted to confirm their reference plane.  It says the reference plane is the ball pads.  Is this the ball pads of the AD9361 package or the ball pads of the Rogers 4003 PCB?  If the AD9361 package, do you know the inductance of the solder balls when mounted to the PCB?

Thanks.