In order to carry out heuristic analysis and tuning, you would still need access to tune, and that comes back to my point around it being made available in an app.
The standard ranging discussed in the documentation I referenced I think gets derived from the details shared in this StackOverflow thread. Note the points in one of the responses about not only the interaction of human bodies causing attenuation, but also reflections from metallic surfaces, and interference from other field generators. I experienced issues around these sorts of interactions when I was responsible for office networking in a previous role; it is sometimes surprising what can impact a seemingly static environment as elements in and around the environment (including outside the building on a couple of occasions with vehicles and equipment parked nearby) can impact what is happening in a particular room. i.e. the location may be static, but what is in and around it perhaps is not.
Fundamentally, if you can configure the iBeacon for a particular power level, this will affect how far the transmission signal will reach, barring any surrounding object interactions (attenuation, interference, reflection). The software on i*OS then ideally needs calibration for a particular iBeacon to determine what RSSI (received signal strength indicator) is suitable for triggering; which is also where any heuristic determination would come into effect, as that analysis would help you determine the triggering figure.
But, when iBeacons are used for in-shop marketing purposes, it is typically the interpretation of the ‘near’ distance identification without any individual device to individual iBeacon calibration that gives the level of accuracy. Assuming no object interactions to impact the signal, this comes back around to the power of the transmission.
If for the iBeacon you are using, you can’t get the power level down low enough to localise the beacon better, then you might simply need to find a different iBeacon that does allow you to get lower, or perhaps some software that allows you to turn down the level further than the software you have used permits. Sometimes command line utilities let you do more than GUI utilities for example.