Quite often, when I am using perfect focus on my archer (or crossbowman), the first kill of a round does not give me back fatigue. I do have the battle flow perk on the character.
I will provide my dxdiag and log.html, though I’m not sure if this happened in the last fight. Sometimes the perk works, sometimetimes it doesn’t. I can make sure to provide the log after it happens if this is necessary.