Hi,
Smaller tanks can use a variety of ways to move the water since the distances are not very large and so there's less loss of momentum. The larger the tank the more difficult it is to keep from getting stagnant areas, especially if the tank is tall. The flow simply peters out and cannot carry CO2/nutrients to the deeper recesses of the tank. In such tanks you get areas that have excellent flow and the plants in those areas do well. Other areas suffer starvation and the plants mysteriously disintegrate or just do poorly. This is particularly true for carpet plants which have the worst of all worlds:
1. They are closest to where decaying detritus settles and where pockets of ammonia develop, with a greater likelihood of producing algae due to a higher ammonia loading rate.
2. Flow rate is lowest here and CO2 tends to rise away from them.
In deep tanks therefore the idea is to force flow downwards against the front glass to ensure maximum contact time. When combined with an external inline diffuser, CO2 enriched effluent is poured down over the carpet plants if the spray bar is mounted against the back wall. Since you want maximum coverage along the length of the tank, mounting the spray bars vertically is counterproductive since this causes a narrow sliver of flow. I've found that if the carpet plants are fed in this manner all the rest of the plants are automatically fed as the the flow is deflected towards the rear and then up along the aft wall. This method allow the water to penetrate even to the floor of the back wall.
In many tanks, tall growing stems have a tendency to lose their lower leaves and it has been assumed that the reason for this is that these lower leaves have less light. I'm beginning to believe that this is only partially true as many of my plants don't lose the lower leaves at all. If these leaves have sufficient contact time with CO2 laden water they can still photosynthesize as would low light plants. Many of my plants retain their lower leaves, even in the shadows. The key, I believe is due to better CO2 and nutrient distribution facilitated by the hydrodynamics of properly mounted spraybars.
The first image below shows the lower half of a 12 inch stem. Peering deep into the shadow area you can see that that this "so-called" high light plant (P. Stelleta) still retains the lower leaves. There is even pearling on the lower side of the leaf surface as the CO2 laden water flows in an upward direction. I never saw this behavior when using lily type pipes, which only send strong flow longitudinally. The second image shows the upper half of this plant (left side of that frame). Compare the relative levels of light from left-top to left-bottom of the frame (note that the first image looks bright only because of the camera's exposure settings.) You can see that although the lower leaves are smaller they do grow and do not shed. In fact, all along the bottom of that image you can see the amount of shading but these plants have no difficulty growing. I attribute this in large part to the spraybar configuration. Again, note that I'm only talking about large tanks. Ed's analysis is for smaller volumes.
In this shot you can see C. wendetii on the right which I prune often, except I pull the lower leaves. The lower leaves on this plant grow out from the shadow area smothering the carpet plants. You can just make out on the bottom of the frame that the P. helferi has little difficult propagating even into the darker areas. Force feeding CO2 via the bars makes this all possible. Now if I could only find some spray bars that do not have EHEIM written all over them.
🙁
Cheers,
This give you the best chance. Anyway, I've completed a self hypnosis course and now I tell myself "what spraybars?" 
). The diameter is slightly larger than the Eheim bar so it's a bit of a struggle to get the Eheim 16/22 hose over it. A little bit of hot water on the hose does the trick. They look a lot better as they tend to disappear in the background. I'm quite satisfied with that (the Gucci glassware fraternity will be rolling their eyes in disdain about now I imagine 