You can also start #1 with something like, "Can you give me feedback on ...?" It's asking an open question and inviting dialogue. "May I know why...?" comes off as though you're trying to avoid hostility, and if there is no hostility, then ......?????
So, something like "Can I get your input on....?" or "Could you tell me more about...?" makes it more of a request for information than questioning a decision.