2cents,
Does the amount by which ACM moves their spread vary, depending on your position size? If so, then what is the relationship? It seems to me that if you can measure the relationship, then maybe you can use this knowledge against them.
Suppose the amount by which they move the spread is the same, for all position sizes. You first take a very small position, opposite to the direction in which you wish to trade. They move the spread against your small position, at which time you hit them hard with a far larger position, your true order, going in the opposite direction.