Thank you! How Cool!
My learning was very empirical, and many of the people I share this tip with, have had a big laugh when they understand they have been trying to speak english with their spanish-speaking face xD...
Americans might not move their mouths very much, but the movements are very specific and different to spanish-speaking people, and it can feel very weird. But once you get others to understand this, is like you were unlocking something in their minds, and everything gets easier.
RE: You can't speak "whale", with your "english-speaking" face"