The first photo shows the backside of the spoiler and the rolled lip. As you can see the size of the lip varies between the two examples. The one with the nice lip is the old one that was replaced and the new one was trimmed much differently, leaving very little lip to work with.
The weak link is obviously the lip attachment, and experience shows that is the ultimate failure point.
I deemed the new lip too small and fabricated mounting tabs, from an ABS flat sheet, that easily glued to the ABS spoiler using my favorite plastic repair/glue Plast-aid.
this time around I also elected to use riv-nuts instead of sheet metal screws. Much more difficult layout than just fixing in place and attaching with sheet metal screws. Not sure it was worth all of the effort.
It is the cleanest of the available spoilers, IMHO