Trading at the bid-ask midpoint and hidden orders

[backtothebeach]

I've had mixed success trading between the bid and ask. On liquid stocks, I often find a hidden order at the midpoint executes, I suppose the counterparty has the opposite hidden order at the midpoint? 

 

IB's midpoint algorithm on the other hand can work, but it feels like the algos react to a larger order and move the price so the midpoint gets worse and worse.

 

Frankly, it is all a bit of a mystery. For example an odd lot (less than 100, e.g. 50 shares) order on FFH.TO does not change the bid-ask at IB on my screen, but I would guess the full order book is visible to other market participants. Round 100 lot hidden orders on FFH can execute, odd lot hidden orders never execute.

Edited March 13, 2025 by backtothebeach

[backtothebeach]

What if someone mentioned on a message board that they had an active hidden sell order at the bid-ask midpoint on a thinly traded stock like ELF.TO? Would that be legal? Asking for a friend.

[johnpane]

You mean odd lot. Round lot is increments of 100 shares.

[backtothebeach]

You're right I confused the two. Corrected.