To determine your baffle height you wanna see what the back flow is when the tank loses power.... If it dumps back 15gal your baffles are gonna be very small.. 5gal you could run them very high etc... Every tank is different... I have the math written down around here some where... No time right now to do it but...
You take LxWxH and divide by 231 ="x" once you "x" you divide the Height by that and get "x" this is x is how many gallons of water per inch in your aquarium.... So let's say it 1.5gal if The bottom of your overflow teeth or return is 3" down from the top that would mean worst case it would spill back 4.5gal.... If that makes sense... I'll try to explain it better in a little bit...

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Ps. Most people will say use a check valve... Don't trust them it's not if but when they will fail...