  When two collisionless plasma shells collide, they interpenetrate and the
overlapping region may turn Weibel unstable for some values of the collision
parameters. This instability grows magnetic filaments which, at saturation,
have to block the incoming flow if a Weibel shock is to form. In a recent paper
[J. Plasma Phys. (2016), vol. 82, 905820403], it was found implementing a toy
model for the incoming particles trajectories in the filaments, that a strong
enough external magnetic field $\mathbf{B}_0$ can prevent the filaments to
block the flow if it is aligned with. Denoting $B_f$ the peak value of the
field in the magnetic filaments, all test particles stream through them if
$\alpha=B_0/B_f > 1/2$. Here, this result is extended to the case of an oblique
external field $B_0$ making an angle $\theta$ with the flow. The result,
numerically found, is simply $\alpha > \kappa(\theta)/\cos\theta$, where
$\kappa(\theta)$ is of order unity. Noteworthily, test particles exhibit
chaotic trajectories.
