You definaly dont want it pointed at the substrate. The idea is to not have anything in a direct jet stream and have everything in a random current. How do you do that? Well ou start with some simple beginning posiions like the back corners blowing toward the middle front with the PH
's blowing one over the other. THen maybe one or two shotting along the back of the tank at differnt levels or one shooting up toward the other side and oen shooting slightly down toward the opposite side.
The idea and goal is good overall flow thats basicly random in direction.