Okay, I made a video about the acceleration and diagonal sensitivity issues and I'll try my best to explain what is happening on screen. The video is 30fps because I used GameDVR, and there's some inconsistencies between the clips because I glued a bunch of them together.
https://youtu.be/K7xH8ZLBCr8
00:20 - Notice how towards the end of the kill I am already moving the stick to the right, but at the end of the kill the acceleration kicks in and my aim snaps to the right.
00:32 - As the enemy falls down, I follow him but can't control the aim due to the changing/inconsistent diagonal sensitivity. Right before I get boosted back up, the aim snaps to the left (when I am right next to the wall) from the acceleration. Once boosted and into the air, now I have to aim downwards but again I don't have tight control over it due to the varying sensitivities.
01:10 - Right after I kill the enemy, the acceleration again is too much and I lose control of the aim. Had that guy not died, I would have over-aimed to the right.
01:28 - This is important. Notice how when I initiate the fight, the guy is closer, and due to the FOV I have to move the stick further when I am aiming. Notice how I miss the shots when he's close, due to the low sensitivity curve (that <30%), but as he moves farther away I can aim at him normally.
02:25 - Very important again. Notice how while I am in mid air and have to aim down, I land the first few bullets. As I get closer to him, I have to aim down and to the right more than when I was higher in the air, but this diagonal sensitivity again makes it hard to control the aim.