Thanks for uploading the pictures, they perfectly explain your concern / issue !.
Yeah - You would expect the bump stops to be adjustable really ?.
But, after looking at your pictures the alignment between the rear quarter and the hatch back lid looks really good !.
But, iin turn if you kick out the hatch back lid any further, you then run the risk of having the hatchback lid, standing proud of the rear quarter panel, which could even look worse.
I think I can see that your concern maybe based around the larger gap between the edge of the hatch and the rear bumper cover is larger and you hope to make this closer.
Honestly, I think this wider ledge is placed there to increase the water drain off from the lager rear hatch.
Trying to push back the hatch back alignment here at this point, is likely to have a negative affect on the body lines / gaps above the highlighted area I feel ?.
Offering no means of adjustment at this point, pretty much tells me that is was not required some how ?.