Local leader supply route question

Ok so i have done a variety of searches in google and here on reddit to find the answer. It has been asked a few times, but i havent seen an answer.

So when you assign a settler to a supply route, it shares your junk(and food apparently). But when you are on said route, does it share with any other nearby settlements on the way? A to C but does settlement B on the way? Or do i need to create a web of travelling supplymen?

Thanks guys!