Line length question,
Odin, a good question, one that took me a while to learn the full implications of, and certainly one that touches upon a deep subject.
Essentially, you need the weight of the fly line to load (bend) the rod which throws the leader and fly at the fish as it springs back, at least on a "regular" cast.
The Yakima River presents situations like that during spring hatches, with fish rising steadily through low visibility water not more than 10 - 15 feet from the boat, but requiring perfect dead drift presentations. A problem develops if you have a "faster" rod that requires a minimum of 20 ++ feet of line in the air to load the rod. You would be better off with a much slower or flexible (and shorter) rod that loads more easily on shorter line.
The bottom line is that you get the fly out to the fish any way you can, and you need to experiment with every way possible to do that. On a river, you can simply slap the fly and leader down into the river upstream from the fish and let it drift down to the fish. Another way would be to pinch the fly between your fingers while exerting pressure on the rod tip to bend it in the direction you want the fly to go, then let go of the fly, flinging the fly forward, like a bow and arrow. This works well for lake or small stream application when trying to get underneath or between foliage when you can't false cast. Hope that helps.