  Huge astrospheres or stellar wind bubbles influence the propagation of cosmic
rays at energies up to the TeV range and can act as small-scale sinks
decreasing the cosmic ray flux. We model such a sink (in 2D) by a sphere of
radius 10\,pc embedded within a sphere of a radius of 1\,kpc. The cosmic ray
flux is calculated by means of backward stochastic differential equations from
an observer, which is located at $r_{0}$, to the outer boundary. It turns out
that such small-scale sinks can influence the cosmic ray flux at the observer's
location by a few permille (i.e\ a few 0.1\%), which is in the range of the
observations by IceCube, Milagro and other large area telescopes.
