If the door is aligned properly and the lines outside match up, you are right, the door mechanism itself does not adjust, the three or four screws are recessed into the door edge so they won't move. Get inside the car back seat with the driver seat laid forward and see if you can see where the door is hitting the striker plate, high or low, then adjust from there. If it is hitting against the outermost part of the striker plate, remove the gasket and see if it clears then, might have to make a thinner gasket. Basically, without knowing where it is touching, adjustments are a guessing game.