  Thanks to tremendous experimental efforts, galactic cosmic-ray fluxes are
being measured up to the unprecedented per cent precision level. The
logarithmic slope of these fluxes is a crucial quantity that promises us
information on the diffusion properties and the primary or secondary nature of
the different species. However, these measured slopes are sometimes interpreted
in the pure diffusive regime, guiding to misleading conclusions. In this paper,
we have studied the propagation of galactic cosmic rays by computing the fluxes
of species between H and Fe using the USINE code and considering all the
relevant physical processes and an updated set of cross-section data. We show
that the slope of the well-studied secondary-to-primary B/C ratio is distinctly
different from the diffusion coefficient slope, by an offset of about 0.2 in
the rigidity range in which the AMS-02 data reach their best precision (several
tens of GV).
  Furthermore, we have demonstrated that none of the species from H to Fe
follows the expectations of the pure-diffusive regime. We argue that these
differences arise from propagation processes such as fragmentation, convection,
and reacceleration, which cannot be neglected. On this basis, we also provide
predictions for the spectral slope of elemental fluxes not yet analysed by the
AMS collaboration.
