Yes I read the karma thing, there is a poster that use this word all the time ,to bad karma don’t bring money in to the table.
About your Q, There is 2 main factor’s; 1. supply & demeaned 2.AON/FOK order have a low order priority on the market and sometime the will skip your order ,in most case small order can be ignore sometime but if you put a big order they wont ignore you again its up to supply & demeaned.
It very imported to learn how to put this order’s so they will fill you most of the time.
I buy on AON/FOK order always on the ASK and not on the BID,I sell my AON/FOK order on most of the time on BID (unless I am not in front of my computer, and if I am off will put it on the ASK). Some trader will tell you no sell on the BID you are not helping the stock, but who cares? you want to take profit and sell fast .
95 % of my order’s on the penny are AON/FOK order I always use them so I wont get partial order ,also for big traders this is the orders to manipulate stock as fake order and lots of them use FOK order