Sorry, but if there have been more clarifications in the thread I think it is important to read them as well. Just to save time.
It is about the layering after dragging: the drag sources were behind the drop target as the OP explains. Which is set up in the snapping section of the D&D panel for the drop target. Layering the drop target under the drag sources in the timeline is not changing that.
I have edited the topic title to make it more significant.