Not uncommon for healthy clowns to hang out on top if they haven't found a comfortable spot in the aquarium, but more common if they aren't feeling well. In the wild clowns have their home in an anemone on the reef or sand and then venture out from that spot to feed.
I have one pair of latz that hang out on opposite ends towards the top of the aquarium above the wave makers. That seems to be their safe spot and they come out from there to feed. In the morning with the lights out I will find them back together on either side of the tank.