If you keep smaller fish that are curious like a longnose hawk they will usually find their way through eggcrate, the holes are just too big.
Here is a picture of the aquamedic overflow combs which are adjustable and well suited for your application. I ended up going with a one piece custom made acrylic comb instead but I suggest you look for something along this line instead of eggcrate.
From this next picture you can get an idea of how the comb styles work & look in my overflow.
