Your overall power for all of your abilities is capped at a certain level, dependent on the strength of your current enemies: For example, if your enemy only has city-destroying levels of power at most, then you will be limited to city-destroying levels as well, regardless of how strong you actually are. It is only when you are fighting an enemy with equal or greater levels of power that you can unleash your full strength.
When not currently in combat, your power instead scales to the strongest individual in the area you currently occupy: If you limit yourself to only operating in a single planet or single region of that planet, your power will scale with the strongest person in the area, while if you expand your operations to an entire solar system or more (provided you are actually capable of doing so), then the power-scaling's range will increase accordingly.