Happiness.txt values are in tenths. Maximal anger should be thought of as 1000, rather than 100, to directly use the values without decimal conversions.
10 troops drop anger levels by 2% per turn. To get the maximal decrease of 20% (if there are no positive anger modifiers in effect), you need 100 troops.
Note that this means that an Urban Pacification Center III is equaled by a paltry 15 small troops... Not that useful of a facility once you undome your planets.
