I think that Proctor's sense of calm resolve is actually demonstrated in the early part of Act III.  Proctor provides a sense of support and determination to Giles, who enters the courtroom in a rage and keeps on proceeding with it.  When Giles threatens to "cut" Putnam's throat,  it is Proctor that reassures him, indicating to him that the path of legal justice is much better than blood vengeance.  I think that you can find much in quotations that show a sense of calm and focus to Proctor.  Some of the very same quotes can be seen in the early portions of Act II, where Proctor and Elizabeth are calmly talking about the events in Salem.  While Elizabeth's tone reaches worry and accusation when Abigail's mention arises, Proctor shows a sense of calm and reasonability when trying to sort through all that is there on an emotional level.  In these sections, I think that Proctor comes across as calm and determined, seeking to find a way out of the social and emotional pitfalls into which he is inexorably drawn.  In these moments, Proctor's focus as the main character is what drives the drama.