I pretty much only adjust droop at the rear of a 12th car to change the on power steering or to settle the car down on a high bite track.
There are a few things that are actually happening when you accelerate to the travel limit of the shock. My personal opinion on why the increased droop increased on power steering is that it raises the rear ride height and rollcenter. I think that the shock acting like a 3rd link (on a real car) is less of a contributor to the steering.
If you draw every thing out, droop shouldn't increase turn in but it does. Again, this is probably because of the higher ride height and rollcenter. The rear end will get held up for a little bit off power because of the damping in the shock. Eventually, it goes back to normal ride height and you don't have any extra steering in the middle.