Sorry your post took so long for answers. As Lynzy wrote, humping can be an innocent form of domination. My Teddy does it occasionally to Max when he is excited or wants to correct Max.
Because of the difference in size of your doggies, I would separate them with an xpen or baby gate when you cannot supervise -- at least until you are confident you can leave them together safely.
__________________ Kristin, Max and Teddy  |