I have always been under the impression, that it was the change of state that actually did the work, and the water traveling in suspension, does negligible cooling weather injected prior to the turbo, prior to the intercooler, prior to the intake or right at the back of the valve.
From the little research I have done on this, if you inject it anywhere but into each individual intake runner, it gets thrown right against the bottom of the intake manifold and pools, and the middle runners (in a cummins app) get a ton more water then the outside runners. In a typical side entry manifold the water that is in suspension gets thrown against the far back wall of the manifold and goes down the last runner, or the heavy water droplets that are failing out of suspension drop in the first runner. Leaving the middle runners rather dry.
To me in a cummins app where the stock manifold is already notoriously bad for providing equal amounts of flow, the last thing I want to do is compound it by throwing water down in that same fashion.
Now I could be wrong on all of this, but this is what I have gleaned from people much smarter then I that have done extensive testing on this...