the bid and ask is 4.10X4.40, I submitted an hidden order to short 200 shares at $4.39, the order was sent to ISLAND. But when I looked at the Time and sale window on TWS, there were 400-share trades on ISLAND on 4.40, but my short at 4.39 was not filled, why? is that because my order is hidden on ISLAND? my understanding is that hidden order is not shown, but if my price is better than NBBO on ISLAND, island has responsibility to fill my order first, then the NBBO price. on ARCA, hidden orders work as I expect, my order will be filled first since my price is better.