Take a look at this picture. It’s from a Russian training manual I have been reading through. Notice in the picture that in the final frame the figure’s torso angle is angled slightly backwards. However, notice it is not angled so far back that the hips are moving horizontally. Sometimes in our effort to be aggressive at the top of the second pull we send the bar away from us by over-rotating our shoulders behind the bar too far. The back should angle a little bit but not so far that your eyes are looking upwards OR the hips are moving horizontally. Watch this video of Matt Hathcock struggling with his back angle at 235#. He made 225# just before this with ease.
When snatching or cleaning be sure that you focus on getting vertical with your shoulders at the top. Don’t let your shoulders over-rotate behind the bar. If you struggle with this try some heavy pulls, tall snatch/clean, or movements from the hip.