Customizing Keynotes and the Keynote File in Revit 

Douglas, It has to do with the Revit family. Try adjusting the 'label text' in the family. Once you have opened the keynote or tag family and chose the label text, Open the type properties and adjust the 'Leader/Boarder Offset' distance. Revit will use this setting OR the linework in the family as the 'setback'. You will also see it with Revision tags. Revit seems to "reach' out the the furthest element in the family and use that as a trim line for the leader. Try using the revision tag (triangle) with a leader and you will see what I am talking about. This is an issue with all families and leaders.