Blackburn tail lights like the 2'Fer, Local and Central have a wide angle of view because they don't use lenses to collimate or concentrate the beams. And subjectively they're just as bright as the comparable Cygolites and others that do use lenses. So the mounting angle is less critical with the Blackburns. I use a Blackburn 2'Fer on the back of my helmet in flashing red mode -- it's very lightweight and lasts for hours in flashing mode.

Also, take a look at the narrow, elongated strip lights to mount on the seat stays. A couple of riders in local nighttime riding groups I hang around with use 'em, and the separation of the two lights really helps gives folks behind you a sense of distance, approach speed, etc. The seat stays on my compact frame hybrid are too steeply angled for those lights, but I plan to get them for my horizontal top tube bike with more upright seat stays, because the cantilever brake cable makes it difficult to mount other tail lights.