I think you're referring to the gonial angle of the mandible? The gonial angle determines how the chin and under the chin appear.

Chin tucking should be more associated the act of swallowing correctly than just walking around or whatever. This is because change may only occur structurally with constant pressure. No one chin tucks for long periods of time and therefore won't change much. It's a meal time excercise.

I believe nasal breathing, lip seal, and tongue posture (collectively called mewing) are far more important. Get that "work" done and everything else will slowly align into the correct positions.

Chin tucking, chewing gum, mouth taping, conscious posturing all "aid" in the mewing method but are fundamentally not doing the "work".