I’m going to presume that Starting Power means the raw unmodified power rating at the start of battle.
Power is colored white, which means unmodified, so 10% of that should be ~220 depending on rounding or truncation.
In-game, when the effect triggers:
16 is far less than 220. 1% would be 22 power, so what is being awarded is less than that.
And so on…
Could a team member double check that the calculation on the Keybelt is functioning correctly?