Wireless power will adjust the range of the RF. Some countries have different laws on this which is why in the Controller menu you have the option of USA max or EU max.
MENU - WIRELESS - POWER - LOW
It is set to 'low' by default. The lower the wireless power the closer the receiver and controller can work. Higher power will allow for a greater operational range (good for drone work) but at a cost of close range.
For the optimal range you should point the Receiver's FHSS logo (on the cap) directly towards (or in line of sight of) the FHSS logo on top of the the Controller. The delrin cap covers the wireless module of both units.
At max power we would expect 1km range in real world conditions.
Please note many things reduce wireless range- obstacles, metal objects, reflections (multipathing) from architecture and landscape, antennas angle (polarisation), interference. FHSS radios (like what we use) are the best at punching through all of that and retaining a good signal, but range still decreases eventually.
Clearly this is not an exact science, but when planning for a shoot we recommend testing the RF range beforehand.
Wireless transmission output power ratings:
USA MAX: 126 mW
EU MAX: 50 mW
LOW: 13mW (default)
*Note that it is illegal to use USA MAX setting in Europe.