I’ve noticed specifically during conventional/romanian deads that from the floor I hyperextend my back, but during lockout I finish with a neutral back.
I didn’t see much on hyperextension from the floor; only on lockout while searching 
Any tips? I did notice this: http://www.T-Nation.com/readArticle.do?id=990092 from the Alpha forum, but I can correctly do all of those exercises with perfect form.