sometimes they will fill a bid where the size is too small to show on L2 and sometimes they will not. It doesn't hurt to try, but there other thing to keep in mind, such as there may be several orders both above and below you where the size is also too small to show. So for example you may put a bid in for 1000 at .50 and I may put a bid in for 500 at .51, and neither are large enough to show on L2. Now if someone enters an order to sell 1000 all or nothing at .45, it should skip right by me and fill your bid. That's just one example, and only the MM's really know what's going on behind the scenes.