I have an old top loader so no idea what line I am supposed to fill i normally just throw in 2 scoops which are just over an ounce (they are my protein powder scoops not the washing powder scoops)
The reason I ask is because I put on a shirt that smelled unwashed. Even though I know that I 100% washed it recently.
Might not be a soap issue but an issue with the water/draining pipes. If it's an older machine, there could be mold/mildew buildup.
Have you ever ran a cycle with bleach or a washer cleaning detergent do clean out the machine?
When I had a washer that wasn't getting all the detergent out it never smelled bad, still smelled good, but it felt like there was a film on the clothes like not all the soap was washed out.