That looks OK. I have the same skimmer in my 16g tank. How big is your tank?
The level of bubbles will change if the water quality changes, like after feeding the tank, or if the water level changes or as the skimmate starts to build up inside the center tube. The lower the water level is on the front grille, the lower the bubbles will be inside the skimmer.
The idea is to get bubbles about where you have them.Watch it for a day or two. If nothing is flowing over into the collection cup, raise the level of the bubble a bit. If you set it so the bubbles overflow into the cup right from the start, in a day they will have filled the collection cup with more water than skimmate. You want the stuff in the collection cup to be kind of dark and scummy water. And during the running, really thick skimmate will collect on the inside of the center tube.