Collar drafting question

I want to draft a Peter Pan collar for the apple picking dress. (I love that dress as is, but this is a special project.) The collar will lie flat against the dress. What I'm wondering is if I can simply duplicate the neckline of the bodice or if I need to make the neck of the collar piece a little larger in diameter. If dresses were made of paper, the same size would be just right, but fabric layers have a bit of thickness, so I'm thinking I might need to compensate for that. I know this is a technical question, but I'm hoping someone will be able to advise. I will also be moving the buttons to the back of the bodice, so the collar will curve inward in the middle of both the back and front -- two bean-shaped pieces. It's just an idea, but I'd like to try it. Many thanks.