Bose Centerpoint- "Surround Volume" setting?

My 2012 CX-9 GT has the Bose Centerpoint Audio System. I have a question about the Surround Volume setting. The settings before it, AudioPilot and Centerpoint, are simple On/Off choices.

The Surround Volume adjustment is only available if Centerpoint is ON. But the Surround Volume setting can be set to (-2) (-1) (0) (+1) or (+2). It is on (0) ZERO by default.

Im clueless about this setting!?!? I could understand it starting at ZERO and increasing, but the negative values confuse me.

The Owners Manual has no explanation..can anyone enlighten me? =)

Centerpoint directs sound levels so that optimum listening area is in the center of the vehicle - basically at the rear end of center console. I keep my centerpoint on and set to 0 - just sounded better. You can tell more of a difference with a good audio source - not Sirrius..

Just my 2 cents worth...