Technically UK lighting regs say it should be centreline or DS, and it's probably marginally more visible, but in practice it's unlikely to make a huge difference.
I ended up going centreline anyway as I discovered the mount I'd made to put the light at the brake bridge on my last frame would work bolted to the mudguard.
Technically UK lighting regs say it should be centreline or DS, and it's probably marginally more visible, but in practice it's unlikely to make a huge difference.