All the SunTour RD's that I've come across do not have a top spring (the one that attaches to the dropout). The adjusting setscrew is supposed to set against either the dropout or the #4 mounting bushing pictured below. That bushing is keyed to fit over the dropout. You have to orient that bushing before screwing the derailleur onto the dropout. I saw something to the right of the dropout on your first picture that looked like the tab the setscrew is supposed to move against. My first supposition is that you need to re-orient the bushing.

Another possibility is that the bushing is screws onto the #2 mounting bolt pictured below. It's possible that it's positioned too far out.