We all know the winter cluster forms on the bottom of the combs and flows upwards as stores are consumed. It is not fixed in position. so the individual bees certainly do move.

Right. Winston elaborates:

Clusters may break occasionally to allow workers to move through the nest and feed. If conditions are too cold, colonies can die even with substantial honey reserves because workers are unable to leave the cluster to get to honey located at the nest periphery (Haydak, 1958). 

Fluctuations of almost 20°C have been recorded, owing largely to changes in ambient temperatures and to workers periodically breaking from clusters to feed. 

The minimum temperature within the center cluster is 13°C, which maintains the temperature of the outer shell at 8°C, the minimum temperature required for workers to cling to the cluster. Inner cluster temperatures are more commonly maintained at closer to 20°C. 

Although workers could undoubtedly maintain warmer cluster temperatures, the rate of honey utilization is reduced by keeping clusters close to the minimal temperatures for adult survival. 

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