“The trajectory of a cast should also be based on the desired casting distance and the anticipated effect of gravity, wind carry, or wind resistance. Ideally, the energy of a cast should transfer down the line and open the loop and leader just before the fly reaches the target…
All other variables being equal, due to gravity, casting trajectory should also vary with line density and the weight and resistance of the fly. It pays to use a higher backcast when casting a heavy fly or high-density line. Even when using the proper pause timing on a cast, these heavier-than-normal payloads will fall faster than a floating line of the same weight with a light fly.”
John Field
onemorelastcast.net 
Say what?
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Which part is your part, mate?
Anyway, I mainly match trajectory to the distance of the target and wind.
Regards
Bernd
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None is mine. I thought that the signature made it obvious. 🤔
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I consider line (loop) speed also as a variable.
The faster the loop speed the lesss the Line will fall over a given casting distance.
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It makes sense. If it takes, say, two seconds for gravity to make the line touch the water, you have only two seconds to reach any distance.
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This is why high velocity projectiles give greater accuracy.
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