I have a group of six and find most of the time they prefer not to be in their shoal. They do have great colour though.
Same here. The males have fantastic colouring, but they don't shoal very much. They like chasing each other around though.
They're quite large fish, bulky fish, right? (At least compared to a same length cardinal, for example.) It could be that it would only be possible to see them swimming in a "school" (or more likely, roughly in the same area of the aquarium) only in something which is say 500 litres or larger just because they may like some personal space. Also having a larger "predator", which is not large enough to eat the barbs, but large enough to worry them would probably make them swim closer together.