Drift, drag, and getting agitated ...

[Silver Creek]

Can someone define or describe "line loop ahead of the indicator" and how that would be accomplished?

I don't know about the indicator part, but I think Daniel's line loop refers to line sag from the rod tip to the point at which the line enters the water. There is NO floating indicator as you think of it. There may be a bright fluorescent inline monofilament sighter that acts as a visual indicator.

The rod tip is downstream of the flies. The sagging line means that gravity is pulling the line down towards the water surface and since the line is sagging and at a slant, this slant causes the line to pull the flies down stream. The degree of the sag determines the line tension pulling the flies downstream. The tighter the line and the more parallel the line to the water surface, the greater the downstream tension. So the angler, by controlling both the elevation and motion of the rod tip downstream, can control the degree of downstream tension.

Modifying my post to address what Warren has said, Gomez's loop downstream is a downstream mend. The loop is both downstream of the rod tip and the flies. Since the loop is on the surface of the water which is flowing faster than the sunken nymphs, this will drag the nymphs downstream and up. Basically this is analogous to a wet fly swing.