They do swim at an angle up and down, but not when swimming straight. I don't raise my rod tip up or down when retrieving, just a slow steady retrieve. If you don't adjust the knot to a little back of the center of the eye, it will loook unnatural on the retrieve. I've had a rosy red I kept in my aquarium I've been watching for months, and I can see why the straight tails work so well
Minnows seem to dart around and swim at various angles, but mostly horizontal
https://youtu.be/gunuGn1pjB0?si=LbSJgQDFIPl9uup7