I know that "could have +past participle" and "couldn't have +past participle" have different meanings when we use them in Declarative sentences, but I think when we use them in Interrogative sentences they have the same meaning. Am I right? Examples: Could you have been nicer at the party? couldn't have you been nicer at the party?
couldn't have in the interogative implies that I think you could have.
could have does not indicate my opinion.
"Couldn't he arrive earlier?" means I think you could arrive earlier next time, and I am asking you if I am correct.
"Could he arrive earlier?" means I do not necessarily have an opinion on whether he will be able to arrive earlier.
This is true for in general for negative interrogatives. They imply my opinion, and are often used to disagree with someone.
"Shouldn't I talk to John?" Means I think I should talk to John, but I want your opinion.
"If I go to London, should I visit Buckingham Palace?" is neutral. I am not expressing my opinion.