Our antennas carry inside an Atheros [More] chipset, then we can estimate better the power/percentage relation we get from iwconfig command.
Then we calculate the distance out of RSSI (Receive Signal Strength Indicator) thanks to this formulae and this paper.
RSSI[dBm] = -10 * n * Math.log(d) + A[dBm]
Where A is the received signal strength in dBm at 1 metre.