Quick ciabatta question

Seems like when I bake this bread free-form ,I can get the nice ,large hole. When I try to do it in a preheated  Corning ware dish with lid on to steam bake, then lid off to finish, it rises nicely, but no large holes. I like the idea of one high large loaf. About all I do to shape is carefully flip the dough into the preheated dish, put preheated lid back on and do it at 475f. No luck doing it this way so far for big holes. The dish is 31/2 quart. Could this be the problem? Too confined?