I don't think the rule applies when you have an overcoat on. At least I never follow it when I do. I always button my jacket when standing but never when I have an overcoat on. It reduces range of motion and causes lots of problems when you have the jacket underneath wanting to be in one position and the heavier overcoat over it wanting to do something else. Leaving the bottom jacket undone allows the two to sort of move in unison.
I really like this outfit. I think the rectangularish belt buckle pushes it into awesome for me. The more rectangular a buckle is the better, I have one that I bought a year ago that's a perfect rectangle, I love it.