Think it depends on the mentality of the dog; my neighbour has a miniature dachshund that chases and barks at everything regardless of size. I know I should not say this but it does make me think was a good reason for choke collars and on the bike the worse dog I have encountered for persistence in chasing me was a white poodle.I'd say from experience that small dog/big dog confrontations are usually caused by the big dog. When out with my mutt i find big dogs being held back by their oh so macho owners, as 'Tyson' tries to get at something an eighth of its size. I see owners of GSD's having to cover the eyes of their dog so it doesn't see a smaller dog and get all het up. Maybe little dogs can sense a much bigger dog's aggression and act aggressively towards them as a defence mechanism.