I guess I did not frame it properly.
Let's use GC Feb-Dec spread. Before Feb expires, we want to make it into a GC Mar-Dec spread.
To do this, we sell GC Feb and buy GC Mar (sell GC Feb-Mar spread). Now, a lot of people also have the same idea and the bid/ask 1 tick and about 10,000 lots. Can you try to sell for ask with 10k lots ahead of you? Hit the bid and pay the spread?
Seems a simple enough thing to pay up the spread. But, I wanted to be sure that AS can't bypass the queue by getting filled via individual legs. ie. the exchange prioritizes a bid/offer the same regardless if it is tied to a spread or not.
But let me run this by you: In a spread with both equally wide markets for both legs, there won't be any miracles. One leg goes for limit and the other one will be a market order when the limit order is filled. That is the only way these things work. Is that correct?