I have the same sump and mine doesn't overflow.I was just telling you to double check cause your setup may be different from mine.I double check everything
It all depends on your water level in your sump relative to the amount that will drain into the sump from your display tank when you lose power. I keep my sump water level 6 inches from the top of the sump. About 1-2 inches of water drains from the display until there's a siphon-break from the holes drilled in my return line. You just have to make sure those holes don't get clogged with algae.