Usually the cluster forms below the stores and eats its way to the inner cover. In my location, they reach the top in early spring. This is why everybody that replied is concerned about their stores - it is unusual for the bees to be that close to the top this time of year.
Additionally, once the cluster is formed, it moves very slowly - that is why beekeepers usually talk about the cluster being in contact with the stores. This means that a part of the cluster is on top of stores (honey, candy board, pile of sugar). Even an inch is a giant distance for a cluster to span during a cold snap.