The range numbers are just estimations, and you should never treat them as absolute.
Think about the range of the Bluetooth (electromagnetic) radio waves as speakers and sound. At any given volume, the sound doesn't just auto-magically "stop" at a certain distance from the speaker. It just gets quieter and quieter the further away you are. Some people might only hear at until X ft, and some people with better hearing might do until 2X ft. (s/people/smartphones/)
How you define "I can still hear the sound" also matters, e.g., if you're talking to somebody on the phone, maybe you still hear their voice, but can't actually tell what they're saying. Would that mean you're still "in range" of the sound or not? Theoretically, yes, but for practical purposes, no? (For beacons, this analogy is equivalent to "if you can detect 1 packet out of 100 at 50 ft, does that mean the beacon has 50 ft range? What if you detect 50 out of 100? 80 out of 100? Where do you draw the line?)
Where you position the speaker/beacons is also important due to reflections, absorption, interference, standing waves, nodes, antinodes, etc. (Just some waves theory! ^_^)
If you want your beacon events to trigger around the 12-ft mark, then just measure the average RSSI at that mark, with as many devices as you can (Android smartphones have significantly different reception characteristics), and make your events trigger around that RSSI.