My setups.
First two photos are on a bike used for day rides, so no rack and a saddlebag. And rarely used at night. Cateye LD1100 mounted at the point where the stays are attached to the mudguard with a steel bridge (the lamp is heavy, and will break the plastic mudguard if fitted elsewhere). B&M Secula mudguard fitting dynamo lamp. One photo with the Cateye on, one with it off.
Second two photos are on my "touring" Raven Tour. Cateye LD1100 mounted on the seatpost (if carrying a pile of extra stuff on the rack that obscures the Cateye I don't bother with it). B&M Line dynamo lamp on the rack bracket. If carrying something large and floppy on the rear rack, this may be obscured, this would be a rare event and more likely with one of my utility bikes that have the same three-lamp setup. Finally, the B&M Secula mudguard fitting dynamo lamp. Again, one photo with the Cateye on, one with it off.
The dynamo lamps are not lit, so the photos only show the integrated reflectors, presnet on both types of B&M lamp.
All the lamps are in the same vertical plane. I dislike side-by-side lamps on a two-wheeler after an experience while I was working as a bus driver, when I mistook side-by-side headlamps on a motor bike for a car a long way away.