I did the experiment running 2 liters 5 times each through a siphon with gooseneck H over liquid level of
..H.. Qavg L/s
My ladder is only 4m high, so had to stop there.
It is just a few runs at relatively low heads with what seems to be not a lot of variation in Q but, if you plot those Qs vs H in Excel and trend it with a 2nd degree poly I can easily imagine that it hits Q=0 at H = 9.1m (29.85ft)
For now I will believe that flow in a siphon decreases with gooseneck height over fluid level, until someone does this experiment with a taller ladder than mine.
Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.