The maxRailDistance property defines the maximum distance to another Widget, where the rail effect is active.
In other words: This defines an area around the other Widgets, where the rail effect uses them.
Example:
If the bottom boundary of your dragged Widget is over y = 50 and maxRailDistance is 100 and
another Widget's top boundary is at 160, this other Widget won't influence the rail effect.
Hold the CTRL-key down to temporarily disable the rail effect.