When I can I make the attachment point as near the CG as posible, maybe alittle forward of it, on the top of the fuse (when posible). I do this on the preditor by putting a hole in the coroplast fin wrer I want to put the string. On scale planes I tie a loop around the fuse infront of the wing LE and attach the streamer to that.

The purpose being to make my elevator more effective. When you attach the streamer to the tail the elevator has to fight it, attached at the CG you only see the drag.

Good luck
Joe