LOL love the diagram. Here is where the art of Prizm tweaking comes into play. The goal is to adjust the hight of your suface attachment and the valve on the input tube so that the water level inside the surface skimmer is like maybe an inch below the water level of the tank (while maintaining the water level at your preferred height inside the skimmer below the collection cup). Get it right, and the top of your water will be crystal clear.
If you don't have a sump, then the water level of the tank will go down due to evaporation and you will lose siphon if you go for a while without topping off. Not a big deal but mildly annoying.