system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars ANH] During the Death Star trench run, why didn't Vader sense that the MF was entering the battle, and why didn't command warn him that another enemy ship was approaching?
gpt
In general, when two potent Force-users clash their 'presence' tends to cloud and distort the Force-senses of the other. This is also, for instance, why Force-users do not simply do things like yank lightsabers out of duelists' hands from the start - it's very hard pierce the natural presence another force user; by the time you can do that, the fight is usually over already anyhow.

Anyhow, trench run is happening and Vader is bearing down on this last X-wing. Unlike all the other Rebel scum he's shot down that day, the Force is strong with this one - he's not immediately able to predict what this pilot is going to do, because his typical senses have been clouded. To line up a shot is actually demanding he actually focus all his attention on this one little X-wing. Have you ever gotten so focused on something your vision narrowed down, your ears filled up with that rushing sound, and all you thought about was getting this one thing done? That's what Vader's having to do.

And then boom, his wingman explodes out of nowhere.

Frankly, it's more a statement on Luke's capability as a totally untrained Force-user that he was able to make the exhaust port shot while feeling Vader's presence.