plantuml-generator doesn't provide classical inheritance/aggregation difference

[Riduidel]

An implicit convention of UML class diagrams is that, most of the time, inheritence is represented from up to down while aggregation is represented at the same level.
plantuml-generator doesn't honor this convention and doesn't even hesitate to put superclass below subclass (in fact, is seems like plantuml-generator doesn't care about that convention).
Could it be possible to add an attribute that would allow this convention to be honoured ?