suppose the bid ask now is 20.01X20.05. I submit a buy order to buy 50 shares at 20.02. since my share is less than 100, the NBBO (bid and ask) does not change. suppose the NBBO bid occurs on ISLAND, but my odd share order is sitting on ARCA. when someone tries to hit the bid at NBBO, who has the priority to be filled? the NBBO bidder at ISLAND, or my better priced bid order at ARCA?