I think the reason Aquamist wants the injectors as far from the throttle body as possible is to allow the most time to cool the intake charge. Where you place the injectors, however, really depends on the application.
If you don't have an intercooler, or have a poor performing intercooler, the best location is far from the throttle body. If the intercooler is fine, it would be better to place the nozzles closer to the throttle body.
Water injection helps detonation in two manners:
1. Cooling the intake charge (also accomplished by the intercooler).
2. By having water in liquid form reach the combustion chamber.
I think #2 is frequently disregarded, but may actually be more important. This is where the water can really remove loads of heat from the combustion process and help eliminate detonation.
In my own application, I installed them in the throttle body inlet pipe.
Check out the website below - in particular the sample installations where you can see where others have placed the nozzles. Good luck!
http://water.lovehorsepower.com