Are the 4 rubber duck bill nozzles adjustable, like the 2 conventional ball ones underneath, and if so how do you adjust them? If they're not I don't want to risk damaging them trying.

 

Yup, push them at their base & they move. There's some sort of solid nozzle inside that you push about.

 

Ahh yes, I can see. At the base of the rubber there is plastic that you can grip with tweezers to adjust. I made the mistake years ago of trying to adjust them like conventional nozzle sticking a pin into the rubber beak. No wonder I damaged one of the beaks slightly.
Also it's impossible to see exactly where they're squirting with the wiper going, so I'll remove the wiper motor fuse when I'm doing it.