What kind of node are you moving? position property changes depending on the type.
I am also not sure why you're using a setgetter for this when you're disregarding the value passed.
I have not used the path with
"../" myself so not sure if it works. I know
get_parent() works though, so something like:
export(NodePath) var pathOfNode
# node path is "Spatial/LEVEL-MESH"
get_parent().get_node(pathOfNode).position = Vector3(0,0,0)