import > add to library > places - each time the same place

When pressing + button last selected folder is chosen.
OK it is no problem when this (last selected folder during last import) folder contains small amount of photos. There is no waiting for “select directory” window (in Windows).
But when this last selected folder contains large amount of photos there is long time waiting for “select directory” window appears.
My idea is to set arbitrary folder which is default when pressing + button.

But which function in LUA is responsible for this folder ?