It is best to have adequate circulation all through the tank. This could require any combination of outlets and power heads. Bottom to top is not really required. Most systems I have seen have no piping below a couple inches of the top. The Calfo closed loop for instance just breaks the surface of the water pointed down in most cases.
I prefer myself to keep the closed loop feed somewhat below the surface so that the surface water (rich in dissolved organics) can go out the overflow to the skimmer without getting mixed back into the main water column.
After the system runs for a bit and you say feed mysis, you will see an oil scum start to form on the surface, now you can adjust outlets to push the slime in the correct direction. You will normally find a dead spot or a collection area that is not where you want it.
