All filters are mad differently so it depends on what kind you have. If you could post the brand and model then it would be easier to answer your question. With my tetra power filters I keep it so that the water comes out a few centimeters above the water line but with my marineland filters I keep it so the water comes out just under the water line. I would look on the instruction and see what it says to do. If your not sure just keep it even with the water line.
All filters are mad differently so it depends on what kind you have. If you could post the brand and model then it would be easier to answer your question. With my tetra power filters I keep it so that the water comes out a few centimeters above the water line but with my marineland filters I keep it so the water comes out just under the water line. I would look on the instruction and see what it says to do. If your not sure just keep it even with the water line.
the higher it is the harder the pump has to work which will shorten the life span of the pump. Your best having it at around the same height.