This process begins with creating a 3D Paint Effects modifier to enclose the stroke tubes that you want to modify. Then you adjust Occupation Volume settings for the modifier's lineModifierShape node to control the spread of tubes inside the 3D region.
To create an Occupation Volume effect
As you adjust settings, the tubes respond to changes in the grid of attraction points inside the line modifier. For more information on the settings, see lineModifierShape node. Consider also experimenting with the interaction between the Occupation Volume settings and the Brush Tube Attributes.