  We study the role of purely external kinematical approximations in inclusive
deep-inelastic lepton--hadron scattering within QCD factorization, and consider
factorization with an exact treatment of the target hadron mass. We discuss how
an observed phenomenological improvement obtained by accounting for target mass
kinematics could be interpreted in terms of general properties of target
structure, and argue that such an improvement implies a hierarchy of
nonperturbative scales within the hadron.
