It doesn't matter about the order in the scene for your test project because only one thing receives signals (which should be the StaticBody2D). Mine is essentially the same setup with the script on the StaticBody2D as follows:
pass # Replace with function body.
OS.setwindowtitle ("Mouse Entered: " + name)
OS.setwindowtitle ("Mouse Exited: " + name)
Ensure that the StaticBody2D is the one receiving the mouse signal information and not some other node. Scroll around with the mouse positioned as required and you should see the window title text change as the mouse enters/exits the collision area as a result of scrolling.