  From the new measurement of F_L at HERA we derive fixed-Q^2 averages
<F_L/F_2>. We compare these with bounds which are rigorous in the framework of
the standard dipole picture. The bounds are sharpened by including information
on the charm structure function F_2^(c). Within the experimental errors the
bounds are respected by the data. But for 3.5 GeV^2 <= Q^2 <= 20 GeV^2 the
central values of the data are close to and in some cases even above the
bounds. Data on F_L/F_2 significantly exceeding the bounds would rule out the
standard dipole picture at these kinematic points. We discuss, furthermore, how
data respecting the bounds but coming close to them can give information on
questions like colour transparency, saturation and the dependencies of the
dipole-proton cross section on the energy and the dipole size.
