I've wondered about Eagleye's theory for several years. I'd sure like to get some guys together and test that out in some clear water with some depth to it. couple of guys to cast, and a couple more to observe what really happens to the line.
What I've been able to see on my own is that once the weight begins "bouncing" the leader soon moves directly downstream of the weight. "Bouncing" is actually the weight stopping temporarily on the bottom until the drag on the line gets great enough to move the weight. If we take any weight, even a 1oz, and drop it in the river, it's pretty much going down to the bottom and staying put. It is only the drag of the water against the line that causes "bounce". Which brings us to another point - the fatter your line, the more drag the water will have on it and the faster it will "bounce". It takes some experimentation to get the right line diameter and weight size to obtain the cast-distance and bounce you're wanting.
Because the weight is stopping frequently, and the hook/corkie/wool is not, your leader is pretty much running directly downstream for most of the run. It is only when the weight starts coming back toward the shore you're on that the line is cross stream. The technique used for Coho and Steelhead of getting the line out in a slot and continuing to let line slip doesn't work the same when BB'ing in the Fraser.