Permenance of symbol changest strength/duration.
Trace in air: Cantrip level
Draw/paint: Leveled spell equivalent
Carved: Indefinite effect. Max number active at one time. If one is active long enough it becomes permanent and stop counting as one of the active.
Runes directly direct the flow of magic. They can allow for the performance of magic in places where it is otherwise unable to be performed.
Possible that other magics cannot be performed, or at least performed normally, in the Planar Void, whereas runic magic can.