The OP pliers are Plate pliers, they are a little different than braking pliers. Yes, the hump goes down, it can be used as a lever against the table for heavy plate to break *up* at the score mark, which is *down* on the plier handle.
Breaking pliers are more freeform , they are used off the edge of the table, or in large holes. Right angle breaking pliers are for small holes. Grousing pliers are for very small cuts where you can not cleanly break the glass into 2 pieces because the second piece is too thin, or where you are making irregular cuts (like stained glass, which is rarely made from square cut pieces) or where you need to chip small pieces off the egde because you barfed up and cut the glass just a tiny bit too big;P
Because breakers and plates are so similar, they are sometimes used for each others actual intended purpose. Both have oversized openings in the jaw, they are designed to start the crack in the glass by squeezing the tips of the pliers at the score mark*, which stresses the glass, thus, pliers with a 1/2 space between the jaws are not for 1/2 thick glass as you might think, but for thinner glass....
*Actully, just a touch behind it, for some reason
