The reason for the 300 foot rule is the communication dance. If the food source is within 300 feet, the dance is a circle. Further, it changes to a figure "8." The problem is the bees will exhaust the food eventually, and then search around in a 300 foot radius from the hives. Any other rich food source will be the other hives.
Ya,I have heard this exact caution about close feeding: so close that a hive is targeted instead of the directed food. Let me point out, when doing a dance, the dancing bee also offers a taste of a given food source so the foragers know exactly what to look for. The question of close distance may or may not have merit. Let me explain what I have witnessed with my own eyes. I have seen a swarm precision move into a prepared hive only 10 feet from the originating swarm hive also of course close food sources.
Ten feet is so close it?s hard to understand how a dancing bee can convey this short distance when one second of waggle equals 1,000 yards. I have heard several beeks apply this logic of time of waggle and close food source and the math does not work for 10 feet or 100ft: 0.01 and 0.1 seconds respectively. However, the bees understand with precision maybe by means that we don?t understand for close sources. If a waggle dancing bee wiggles its antanae does this mean anything? Is there a means of conveying short distance in lieu of the waggle??? we do not know, but that does not mean there is not another method for short distance.
I just try not to place food next to a hive, say within 20 ft of a strong hive. Also consider I am a hobbyist with max 20 hives. I do not know about feeding with 100 plus hives such as many on this site.
Cheers