Ender: I agree, this halacha is pretty straightforward. The OP is funny when he says he’s looking for mareh mekomos. Maybe he should start with siman 89 in S”A (orach chaim btw) and then move on to the M”B on that siman.
When he finishes all that he should look back at his question in the OP and explain to us all why he shouldn’t be able to rely on maran in seif 4. Unless he wants to claim that he’s not looking for kulas whereby he shouldn’t have given possibility B for that is definitely being more meikel then seif 4.