I can try. Basicly all I did was take a jigsaw and cut about an inch off. I wish I would have cut a little less but since my fish are mostly pretty big it isn't a big deal. I also wish I would have cut every other space out. Since you are keeping smaller fish I would recommend taking a little extra time and cut out half (longwise) of every tooth and see how that works. It should provide plenty of flow but still keep your fish from going into the overflow box.
I wish you didn't have this problem but at the same time I'm glad to hear it isn't just me. I just don't understand how those little slits could possibly allow enough water to get through to the overflow.
Make sure you cut slow. If you cut fast it just melts back together.