I assume they are intending the term "added weight" to indicate weight attached to the leader system and not the actual fly line itself. An added weight and long leader can be drifted horizontally down stream, mended to insure a drift. With weight on the leader and a weighted fly on the end you could basically keep several feet of leader drifting sideways, a few inches off the bottom of the river. Anything that the leader catches on the hook will drag across. Another of the fine fishing techniques probably created in Arkansas. Surly they are not intending to limit the distance between a sinktip and the fly to 4 feet. But, since I have heard they have now limited 30 miles of the Umpqua steelhead area to "dry fly only", I guess anything is possible.