I used the new Cinch the first two weeks in May on vacation and it worked terrific. I used the 100-400 but with no hood, but I've never been able to get it to sit right on my back. I have the strap connected to the top left of the camera when looking at the back and the other end is on the right strap lug on the bottom portion on the L-bracket. It hangs on my right front towards the side and seems pretty snug. I'd love to try it hanging on my back if I can figure out how to get it to do that.
Try connecting it to the right factory bracket and the right L-Plate bracket.
Connecting at the top Right and bottom Left, you get this triangle effect where the corner of the camera presses against you, so it never hangs right and gets super annoying. We've found that just connecting both ends of the Cinch to a single side of the camera works pretty well to fix this.