Once the auto-calibration is run you shouldn't need to touch the volume control on the sub. That setting is the right one for your receiver. You may be able to dial in a little more bass from the receiver, but it really shouldn't be needed.
Maybe you're used to really boomy bass. With smooth, accurate bass reproduction the subwoofer shouldn't call attention to itself. It will just sound like all the speakers in the room are reaching lower than they normally can.
Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs