Yes, we're on the same page. The tension in the upper loop is high when you're pedaling hard. Coasting it's equal to that of the lower loop, and when back pedaling it's equal to the lower loop less the resistance offered by the freehub.

If the upper loop sags significantly when you coast it means that there's excess drag in the freehub which is trying to push the chain forward, spooling slack into the upper loop. If it doesn't sag coasting, but does when backpedaling than the drag may be in the RD pulleys.

You can do a quick test of the freehub by removing the rear wheel, and spinning it forward in your hands. Put a finger against the cassette and it should take near zero force to stop and hold it. If the cassette feels like it wants to turn with the wheel, it may need to be serviced (cleaned and lubed). BTW- sticky freehubs are very common in bikes ridden in wet conditions.

Going back to your earlier post. I doubt this problem was caused by the shop, and was more likely something developing over time. It might be related to whatever caused you to replace the chain the first time though, and it's disappointing that the shop didn't notice. Even if the shop is 100% blameless you might consider taking your future work elsewhere. There's nothing worse than having to depend on a mechanic you don't have confidence in. It isn't about his skill, it's about your comfort.