You have asked about the comission for IB AP trading is higher then that of normal trading the best way to find out is to get maximum research in the field of trading and such things, visit various articles and to get yourself updated with such types of processes.
Instead of all the guessing, I asked IB about this. Even if you're on tiered, your directed API orders are on the fixed commission schedule, meaning you'll pay 0.0075. That's what I understood beforehand also by simply looking at commissions of executions. "Alessandro B: Fixed - US API Directed Orders: USD 0.0075 per share (see: https://www.interactivebrokers.com/en/index.php?f=1590&p=stocks1) Please note that directed API orders cannot use the Tiered fee structure. Smart-routed API orders can use either the Tiered or Fixed structure, see Note: https://www.interactivebrokers.com/en/index.php?f=1590&p=stocks2 a*********: I've found the page Alessandro B: The above note is at the bottom of the page a*********: hmm, so while I'm on tiered, API directed is charged based on fixed? Alessandro B: Exactly"
Note that it's not absolute. Just a week before I had a chat with Angel from API support and he gave me wrong information. Alessandro seems more knowledgeable though.
Since IB doesn't take PFOF and they're no longer in the market making business, why do they want to discourage the use of directed orders so harshly? at 0.0075 per share it's basically prohibitive.. and in the tiered fee structure I don't see any reason why they would care. Is it so that they can internalize orders to subsidize other clients and improve their price improvement statistics?