@LarsMeiner if it was really driving me crazy I would just micro-adjust cable tension using the barrel adjuster on my rear derailleur. Turn the barrel adjuster clockwise to move the jockey wheel away from the trainer. Turn the barrel adjuster counter-clockwise to move the jockey wheel toward the trainer.
You can get behind your bike and eyeball the cassette cog and the rear derailleur jockey wheel while you turn the barrel adjuster. Just turn the barel adjuster until the jockey wheel lines up with the cassette cog.
