Here is data that is very detailed about the clustering of bees:

THE THERMOLOGY OF WINTERING HONEY BEE COLONIES

By CHARLES D. OWENS, Agricultural Engineering Research Division,
Agricultural Research Service

All tests were conducted at Madison, Wis., from December 1 to March 31 for 5 years.


http://www.beesource.com/pov/usda/th...lletin1429.htm

SUMMARY

Thermocouples were established in different planes in a hive of wintering honey bees (Apis mellifera L.) at Madison, Wis., and temperatures were determined. Then the colony was killed with gas. Exact determination of the cluster location in relation to recorded temperatures proved that such temperature records precisely locate the cluster and show where brood is being reared, where bee activity occurs beyond the brood area, and the insulating shell of relatively inactive bees.

From 1,200,000 thermocouple temperature determinations made in beehives during the winter, the following information was obtained:
(1 of 20)

(1) Temperature readings permit determination of the cluster size, shape, movement, and brood-rearing activities.

Regards,
Ernie