Clown fish will sleep at the water surface on their sides. The current just happened to carry them to your over flow box. They look quite pathetic when they are in that state. If you want them to sleep well, they need something to host in. You could get an anemone and or corals that feels like anemone for your clowns. They will then sleep in their host and not float to the top.
The behavior you describe is normal for clowns. I would not worry about it.