Actually, Harpoon has a deadzone when you are within 5 yrds of a target, so you usually want to harpoon into the target. Disengaging into the target wouldn't make any sense, because then you have no escape for 20 second and a dead skill in harpoon unless someone is standing away from you that you can harpoon to, which isn't guaranteed.
Disengaging in would only make you look like a fool.