We discuss the theoretical basis for relating the mean ortho-positronium (o-Ps) lifetime to free-volume hole sizes using a finite spherical potential well model. The status of the localized o-Ps atom in amorphous polymers is evaluated by calculation of the o-Ps barrier transmission probability. The results indicate that the relative probability for an o-Ps atom to remain in a particular hole during its entire lifetime is on the order of 10(-2). We conclude that there is no justification for a one-to-one correlation of o-Ps lifetime components with specific hole sizes.