Beacon: dBm power decrease over distance
When you have clear line of site (no obstructions), you will get 1/4 the power (6 dB less) every time you double the distance.

So in this case you would get -59 dBm - 6 dB * log2(range / 1 meter) or -59 dBm - 19 dB = -68.5 dBm

For much more info on this, check out: https://en.wikipedia.org/wiki/Friis_transmission_equation