Ok one more try, but i am going to leave it at that…
This time with Position Pass to check which pixels can be read from:
edit:
A nice side-effect should be that any geometry that is added to the scene should render just fine, as it will be ignored due to not being recognized by the position pass.
Also this scene is very ‘friendly’ to this approach, as most of the contributing surfaces are visible. Did a few more tests where more is occluded == less paths can read from the buffer and the quality gain went down fast