As we learned in the Cornell Beekeeping Course, feeding hives syrup indiscrimately or letting them clean honey in supers must be done at least 150 feet away from the bee yard.
This is because the bees are better able to give direction during the waggle dance for distances greater than 150 feet. If it's less than 150, they'll start looking nearer the hive and that can stimulate robbing.

Jean-Francois Lariviere
BeeHealthy Farms, Inc.
NY NY