Are you sure your screen brightness is above 25% with out the Smart Action activated? I know I keep my screen at 0% brightness (the slider all the way down) most of the time and the smart action does make it brighter. To make the Smart Action dim the screen more, tap on the screen dimming action module and turn the slider all the way down.
Hope this helps!
If your usual brightness is below 25% then "dimming to 25%" will actually raise the brightness level. Try setting it at 10% or lower my everyday brightness is only around 20% now so it would go up 5% with the rule.
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