We did JTA last week. I had my son line up on a circle in the front row, directly in front of the rope, based on the advice I got here on DIS, to try to get Vader. There was a second row of circles against the wall. When we got there, most kids were trying to get on the front circles. No one wanted the back circles it seemed.
However, when they had the kids line up to walk over to the stage area, they let the back row kids line up on the "right" side, as if they were in the front row, so I had a sinking feeling those kids would get Vader. A few parents quickly moved their kids out of my sons row into the other row, obviously thinking the same thing, but I didn't bother.
We ended up getting 7th sister. It was still a good experience, my son enjoyed it.