Hi,
The flow dynamics within each tank will be very different and there isn't really a one setup suits all system that will resolve all the issues for everyone. IMO having even flow distribution throughout the tank is the hardest of all the things to achieve.
There are a lot of variables like how many inlets/outlets, amount of flow, physical dimentions of the tank,size and position of hardscape, planting density, type and size of plants (some prefer more flow than others). The list really goes on and on. So much so in fact that its almost impossible to generalise, IMO.
Having the spraybars facing foward from the back wall is the preferred method of many but it would appear that you will need a reactor on each return to achieve even distribution of dissolved co2. There was another thread discussing exactly this a short while ago.
http://ukaps.org/forum/viewtopic.php?f=38&t=10079
Aesthetically though this arrangement doesn't suit everyone myself included and I aim for the flow to be in a circular motion along the length of the tank to try to achieve a more natural looking riverbed with the residents prefering to face upstream more often than not.
I achieve this by having two external filters whose inlets/outlets are at opposite ends of the tank. One spraybar is just under the surface and level and is aided by a koralia 1 to push the surface from left to right. The other is about 4" under the surface and points about 30 degrees up from vertically down aiming right to left.This is the co2 enriched return. Above this second spraybar is a Koralia 2 powerhead also pointing down and accross the tank (right to left). Both spraybars are cut to fit across the entire width of the tank and the koralias are on the same timer as the co2 solenoid valve, therefore when the co2 is on the tank turnover is raised to about 25x the tank volume and the co2 enriched return is forced straight down onto the substrate. I have found that I do really need the extra flow (i.e. 25x instead of 10x tank volume) from the koralia's to really 'push' the water the length of the tank though.
This arrangement will not suit everyone but it works for me.
Regards, Chris.