On that I have no idea. Are you making different syrups for one carbed up water fountain like the old times, or bottling up different ones?
If your bottling, I'd say just use the orange juice whole. Otherwise you are going to have to experiment, or look up on how to do a reduction. Maybe a chef would be able to answer this.
Maybe you should try picking up some orange torani syup and try it out, then attempt to replicate or expand on it. I'm guessing the ph of oranges/syrup/ and sun kiss may be the clue to how much you will need.