The easiest way to learn to cant the bow, head and string hand is to bend at the hips.
Bend at the hips, not the head, neck, or upper body. Shooting up hill the shoulders are parallel with the hill, shooting downhill the shoulders are again parallel, maintaining a "T" with the spine and shoulders. When bending forward to cant the bow think of maintaining the "T" by bending at the hips. You don't want to bend the spine like a "(" on one shot and not the next. Maintaining the "T". Your anchor, and distance between your eye and your anchor will be more consistent. Raising or lowering your head (eye)is likely the cause of missing. Things become inconsistent when we start bending just the neck or upper body. It becomes even more important if you want to shoot at moving, running or flying targets. If you have shot a shotgun you learned to swing, or pivot with the hips and not the upper body.