I think that if that fellow had been allowed to expound a bit more on his 'too big' theory, it would have made more sense to you. If you have your babies in a wide open space with no hiding places, they might be a bit stressed because they are prey and feel too exposed. Add a bunch of 'furniture' into the space and see if they don't start to grow better...things the babies can hide under as they go from place to place.