Yes, it is designed for a rimless tank. My tank with the Eshopps mounted all the way up to the bottom of the black trim results in the water level being about 1/2" below the black trim. At first it bugged me; now it's just the way it is.
If you fine tune your siphon with a gate valve so the water level in the clear box is right under the emergency pipe the pressure will keep the water higher than the bottom of the overflow teeth. I have an eclipse S on a 40 breeder and the water line is above the trim.