The plant hangers suspend it out far enough from the wall that the whole tank is lit. The fixture isn't touching the tank at all although the angle its shot from may look like it is. That fixture is maybe 7" wide over a 18" deep tank and suspended about 6" from the water surface. (I had to do this because it's a 30" fixture over a 36" wide tank.)
If the tank is in the middle of the room and hanging from a ceiling isn't an option, you can suspend it from a canopy or cut a hole in a canopy where the fixture sits on a lip. Look up Mr. Saltwater Tank TV where he reviews the Radions to see how he made his canopy.