Option 1. You can now highlight the action that the new action should be displayed under, as per the image below:  
      Step: Highlight an existing action -> Click on Add Action. The new Action will be displayed below the selected/ highlighted action.

Option 2. The Add Action dialog displays a list of the existing actions, you will then select the action that would be used as a reference to display the new action.
             Steps: Click on Add Action and select an existing action from the list Save.

Option 2 can also be used to update the location of an Action within the list. This can be done by double-clicking on the Action or by using the standard Edit Action functionality then selecting the Action that would be used as a reference.

Further, note the order on the chart is maintained on the list and to optimize the functionality we recommend saving the chart every time you add a new Action.