In surround ES2 instances, two additional parameters are shown in the slide out Extended Parameters section at the bottom of the plug-in window: Surround Range and Surround Diversity.
Surround Range: Determine the range of the surround angle (0 to 360 degrees). Put another way, this sets the breadth of the surround field. You can modulate the movement of sounds within the surround range by using the Pan target in the router.
Surround Diversity: Determine how the output signal is distributed across your surround speakers. If you choose a value of 0, only the speakers that are closest to the original signal position carry the signal. A diversity value of 1 distributes an identical amount of signal to all speakers. You can modulate the distribution of signals between speakers with the Diversity target in the router.