TDI,
There are no real absolutes because it all depends on the internal geometry with the hardscape and plants and size of tank. In my tank, due to the large size I found that mounting the spraybars on the back of the tank improved my ability to grow carpet plants substantially, and I found that the other plants responded as well. Plants which were CO2 critical such as Ammania in the mid-ground grew much better. In a smaller tank, or with a different internal configuration, or even with a different set of plants I may not have seen a difference.
Just try different outlet combinations for a few weeks at a time to find the best for your particular tank. You ought to be able to see the flow patterns immediately by noting the movement of the leaves on each of the plants.
Cheers,