I think a little courtesy can go a long way, and personally would have worked with you to reach a mutually accomodating storage solution

That said, they do say that your primary storage space is under the seat in front of you. Further, I typically try to board as soon as possible (without getting snagged for a supplemental search) for the specific purpose of getting my pick of carryon storage space. This is another reason why flying on the upper deck of a 747 is so much better than the alternatives.