  We investigate the predictive power of transverse-momentum-dependent (TMD)
distributions as a function of the light-cone momentum fraction $x$ and the
hard scale $Q$ defined by the process. We apply the saddle point approximation
to the unpolarized quark and gluon transverse momentum distributions and
evaluate the position of the saddle point as a function of the kinematics. We
determine quantitatively that the predictive power for an unpolarized
transverse momentum distribution is maximal in the large-$Q$ and small-$x$
region. For cross sections the predictive power of the TMD factorization
formalism is generally enhanced by considering the convolution of two
distributions, and we explicitly consider the case of $Z$ and $H^0$ boson
production. In the kinematic regions where the predictive power is not maximal,
the distributions are sensitive to the non-perturbative hadron structure. Thus,
these regions are critical for investigating hadron tomography in a
three-dimensional momentum space.
