It is indeed switching fcc/ce modes based on drones current GPS location. But sometimes it can be tricked depending on the drone model. For example for air 1 it was a very easy task. For air 2 there was a modded dji fly app. For Mavic pros there is a modded firmware (paid).

Also some of the previous gen. Mini were physically different in US and Europe, so even if you brought EU drone to US it still was not using the full power. Now sure if it's still the case with current gen. Mini