Phobos I think that in the large adders it is an accidental feeding response. I have 3 B. rhinceros and 5 B. nasicornis in one cage and no problems to date.I suppose if I only had one of each then they would kill each other. You know how Murphys law works.
The small bitis are all lizard feeders and I think many of the strikes are instinctive thinking the bit they can see is a lizard.
Small female Horned adders are just grumpy things and like killing and often eating the males.