Under the same rock as the larger hairier ants seen in the previous sighting (4731426) and shown with these in the last photo. See the other sighting for details.
And following on from the other sighting, I'm also happy these are all the same species of ant despite the variation in size of the individuals. Some types of ant are monomorphic, having virtually all workers more-or-less the same size, but some are polymorphic and have workers which can vary widely in size. Cheers, Jon