I'd already explained the shunshin no jutsu in one of your threads if i remember correctly
Notice that in the definition of the technique,
it says to an observer, it appears as if the user has teleported, but in reality it's not the case. It's just that while using Shunshin the user boast his own body to move at a high-speed movement
The capability to perceive the movement of a user when Shunshin is involved then depends on the speed of movement in question when the body is revitalised in chakra, the distance seperating the shunshin user and the observer as well as it's observation and reactive capacities(if he wants to dodge or counter)
Example1
Sasuke vs Team7
Notice that Yamato was capable to follow Sasuke's shunshin speed(bottom left panel) [
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] noticing the speed of his shunshin(
he is fast) [
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] when Sakura didn't(when did he?)[
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]
The distance seperating Sasuke and team7 is roughly between 4 or 5m.
S = D/T. Greater the distance and smaller the time, greater is the speed. Concurrently, smaller the distance and greater the time, smaller the speed. Just like the speed of someone covering a small distance in the same amount of time as some other covering a greater distance would be smaller
This is basic calculation maths
So if for example, on this picture Sasuke covered a 5m distance in 1s, it would mean his speed is 5m/s. But if the distance between them was 10m instead, it would mean that with a speed of 5m/s, Sasuke would cover the distance in T = D/S = 10/5 = 2seconds. If the distance was 20m, Sasuke with a shunshin speed of 5m/s would cover the distance in T = D/S = 20/5 = 4seconds
And like you can see, with a speed like this one greater the distance and longer the time it takes Sasuke to cover said distance, and longer the time it takes for him to cover and more the time it gives to an opponent to observe him
Sasuke against team7 covered a distance of 5m so fast for Sakura eyes to follow. Yamato could follow it however. It simply means his observation skills/speed and analysis was greater than Sakura's here. Because of this, he had more chances to dodge/counter Sakura's shunshin than her. And since he was capable to follow Sasuke's shunshin from a 5meter distance, greater the distance and easier would it be for him to dodge or counter it no problems
Example2
Sasuke vs Deidara
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Like you can see on the picture, the distance was roughly 7m, probably more since Sasuke was inside the crater though. So from this distance like represented on the picture, by revitalising his body temporarily with chakra, he covered the distance so fast that it surprised Deidara(
"so fast"). But notice that Tobi(who was near Deidara) had no
exclammation mark on him, showing he had no trouble following Sasuke's speed(maybe because he already saw greater speeds before lol), to the point he was even fooling around, making as if he was hit by Sasuke
So this is basically how a shunshin movement works