You can choose whether to control volume by velocity, modwheel, or both.
To set the velocity and modwheel volume, choose "Set velocity volume, and modwheel volume controls." from the "SETTINGS" menu.

Now, we can set the velocity volume...


...or the modwheel volume



Higher values increase the dynamic range of the control. For example, a value of 0 effectively turns off the feature and you get the instrument at full volume. A value of 9 has a dynamic range of completely silent to very loud. A value somewhere in the middle cuts off the bottom range of the dynamics.