I do prefer always using self.attribute, it’s a little bit longer but there’s no ambiguity. Otherwise you would have to have all props in your head when reading the code.
For considerably long methods you are correct. But the rubonic ideal is shorter methods, and for such short methods, it doesn't provide much in the way of reducing cognitive load. As a reader, if you see no assignment prior to the access of the "prop", then it is a method. The problem comes when you can't fit the whole method on your screen, which is a pretty good rubric for whether you can fit the whole method in your head.