In using the sub-unit and sub-x2-unit I would imagine that if you use say sub-x2-uint and the use is assigned to an Orgunit in hierarchy that has only one level below it would assume the sub-unit level.
An example is where on the learning land:-
We have (National, Region, District, and Facility)
While at national we want to use sub-x2-unit so that the national user sees districts and use the same charts for a district user to see facilities
For this chart using sub-x2-unit, the national user sees districts, but its blank for a district user, is it because the districts has no sub-x2-unit?