By pointing down, I was referring to a 45 degree down angle toward the front. This would never put the aircraft in the "silent area" unless the TX was held up. Most manufacturers are vague on antenna position, other than "don't point at aircraft". If earth acts as a huge ground plane, then you would certainly want it pointed strait up and try to avoid flying high overhead (which sometimes happens at aerobatic contests). I think the antenna angled to the side would be great for pylon racers.
If only we could rent data loggers to capture frame errors and run some tests of our own!
-DJ