Ok guys, thank you very much once more. I see I have to study much more
phonetics in order to truly understand it well. I recognize now there are subleties which may depend on the locale one speaks English.
Raymond: Nobody told me that - I just observed native american speakers
pronouncing them differently.
Thank you all for the important contributions.
I toyed with using the term 'alveolar ridge' and thought better of it. (Hard as it may sometimes seem, - - I try not to use big words in a teaching forum [I thought this was Ask a Teacher - bit of a rush]). My point - poorly made - was that the point of articulation was not moveable.