Right, overflavoring can lead to no flavor. That's one of the reasons I wrote my flavoring level blog. It's a "can" and not a "will" because it's not absolute. Tobaccos flavoring, as an example, doesn't tend to do this. Many tobacco flavorings actually change taste to something COMPLETELY different with different levels. (So different that you think you mislabeled your bottle or something.) The tobacco I'm vaping now works at this taste from 3.2 to 3.6% and changes to something else below and above that zone. The others tastes from this flavoring aren't bad, but I like that 3.2-3.6% zone because there is a whole bunch of subtle notes that organize together to form the perfect taste for me.
DaMutha's Sweet Tart recipe is like that. The overshoot in flavoring results in a different taste than if you were to use it at a lover level. I've never found it to steep out.
TPA/TFA's sweet tart makes a good smarties at about 10%. I've been playing with it to give the same effect as the powder that is usually on them, and while I've gotten close, it's not perfect yet. If you like Smarties then it's a great choice and easy to hit a tasty vape without any hoops or tweaks. I still like it even without the powder effect and sometimes mix a bottle of just 10% sweet tart and go.