Rail Mounted Light & Saddle Bag?

[Powely]

Just looking at lights & saddle bags and wondered if anyone could shed some light on a query I have. I'm thinking of a Cateye Rapid 5 with the Cateye saddle rail mount and wondered if I could still fit a saddle bag with the light when it's rail mounted? I am thinking there should be enough room but I'm not certain?

Thanks

Al