Originally Posted by
Maelochs
Well, it helps to mount it on the roadside seat stay.
There are all kinds of clamps and straps for mounting lights .... yes, you need to angle the light optimally for optimal visibility (which is why I don't like clipping the light on my seat bag, where it invariably points a little downward) so just do a little research on bicycle tail light mounts and choose what you like best.
This. I have never seen a light mounted on a seat bag that was properly aimed. They all seem to flop around.