groupSizeHard1_6 constraint doesn't work - it aimed to make sure that each of the facilities is used at least once.
However when tested in separation from other constraints it ended up putting all the allocation on one beamline. It did not make any change whatsoever in the final solution.
I don't think we really need to add a constraint for this given the problems we solve tend to have smaller capacity than needed - lots of students and few sessions. We already have a constrain that reduces the variability of the group sizes - which have similar effect.