A 20% focus miss rate on portraits isn’t ideal if the only issue is autofocus accuracy, though it may still be a normal overall keeper rate. How acceptable it is depends on light, subject movement, camera AF performance, and technique.

To improve your hit rate:

• Select a specific AF point yourself rather than letting the camera choose.
• Place that point on the eye and use continuous AF if the subject is moving.
• Avoid focus-and-recompose for close portraits, because recomposing can shift the plane of focus enough to move sharpness off the eyes.
• If misses are consistent, check for front- or back-focus with that lens/body combination.
• Expect lower hit rates in poor light or with a slower/less reliable AF system.
• Practice tracking moving subjects; portrait work with active models benefits from skills similar to sports shooting.

So: some misses are normal, but if around 1 in 5 images consistently focuses on the wrong facial feature, it’s worth reviewing AF point selection, technique, lighting, and possible calibration issues.