Spent some time experimenting since this last post.
The 'tick' seems to be caused by a combination of gravity on the extended line, the angle of the stopped line on the backcast, and the whipover effect as the loop comes straight.
Continual tension by tilting the loop
When the loop comes straight the tension comes out of it until the forward cast re-establishes it. In this transition gravity can get hold of the line and pull it toward the ground. By tilting the line sideways the line stays in more of a continuously tensioned ellipse (slight) and thus is less susceptible to gravity, staying aloft in motion kind of like the infinity symbol.
Angle of stop
It doesn't take a rocket scientist to notice that the backcast angle should be inclined upward to help provide room for the transition. Over-emphasizing this works against, but a little goes a long way. Also, a firm positive stop position (as John Wilson mentioned) is important.
I removed the leader and observed the whip-over effect. It was dramatic but could be controlled by easing the start of the cast. In a sense it was good practice, but there were a few snap-crackles and pops when I went for distance and the end of the fly line was frayed out after a few minutes of trying for the backing.
I snipped off 1/4" of the fray and re-tied the leader. Immediately the softening of the turnover at the end of the line is felt. It's absolutely clear that the leader plays a large role in containing the whipover effect.
Some lines were more susceptible than others, I believe based on the leader observation that this is a function of the front taper whereby the longer and more gradual the front taper the less prone to falling to earth during the transition. This is just hypothesis at the moment and I will play around a bit more to find out.
In any case, I took a two-hander out and overhead false cast a 75ft head spey line back and forth on a 14'4" rod and it appeared that these factors were influencial in whether the line ticked the surface or remained aloft. The two-hander cast overhead really emphasizes things.
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