Think about it. IF all the weight was concentrated over one side, lifting the box from one side would give a very much different weight than from the other.
Just like see-saw - if all the weight is over the fulcrum it will balance whatever the weight might be, but a small mass at a greater distance fom the fulcrum can balance a greater mass coser to the fulcrum.
In the case of the see-saw, the weight of the two masses would have to be weighed just under the centre of mass, while only that mass was installed- this assumes, of course, that the see-saw mass was negligible.
Really simple when you think about a simple scenario with extremes of where the weight is situated.
If the weight is taken from both front and back, as well as the sides, the beekeeper could work out where the most stores are situated (not in all scenarios, mind) and thus knowing where the cluster is situated (IR in the depths of winter, or uncappings drop at any time, the situation within the hive,with regards to stores and cluster, could be logged to guard against finding the cluster isolated from the stores. I would never bother to go to those lengths, but it is possible!