completely submerged

I see in some pics there is a water line on the box. Does the water have to always be lower than the line or would it harm the boxes functionality for the water to ocassionaly lap over it? I have watched the videos on Tunze's website and they clearly show a wave box that has a very thin layer running over the top at each cycle. Just wondering because my tank is completely inclosed with only two large opening at near the center. If I was to place the wave box in the back corner pointing length wise I believe it will get completely submerged during the sway of water.
 
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