our robot, trogdor, can shoot high or low. when we go for low, we line ourselves directly up on the side of the tower and hug it. we've had extremely good accuracy with low goals, and when shooting high goals, we place ourself 13-14" from the high goal, a little distant from the defense we just crossed. my distance estimate may be off by quite a bit, however. sometimes we place ourselves directly on the skirt of the tower in front and shoot high.
here's a video:
https://youtube.com/watch?v=aJFSEiNU3DA