*Sometimes you may need to increase the "Max Density" to make the stacks closer, but the "Horizontal Distance" is the right control for that.

*The "Vertical Distance" control the distance between each instance in the stack. This is useful when you have instances with different height.

*If you set the "Random Position" and the "Stack Twist" to 0, the instances will get perfectly aligned.

*The "Surface Offset" moves the instances above the surface object and can be used if they are overlapping the surface.

*The "Base Disorder" randomly spreads gradually the instances that are closer to the surface

"You can paint a vertex group and load it on the "Mask" input to control where the instances will gonna be generated.

"The "Surface Spread" scatter some instances around the piles on the surface object to make it look more natural.