Water takes the path of least resistance, much like electricity. You have a narrower exit at the top, therefore water is more restricted there. Also, you are fighting gravity. But the water around the pipe will apply pressure to the water in the pipe, and the top is outside of the water or higher up so less pressure. So, if the pressure of the water pushing down is greater than the pressure in the pipe, then water will be sucked into the pipe at the middle and taken to the top. If the pressure in the tank is less than in the pipe, then water will flow out the middle. If the pressure in the pipe is low enough, ie close to off, then water in the tank will have enough pressure to push against the pump and flood the sump. I'd say this is a bad idea, mostly for that reason alone. I'd have just the exit at the top and if you want greater water movement, use a spray bar or some fancy nozzle.