SFX is an independent exchange company, so in most cases, they don't receive bulk space banked weeks from resorts.
Most of the larger resort systems are affiliated with RCI and II, so they are contractually obligated to do their bulk space banking exclusively with RCI and II.
SFX's inventory comes from individual owners depositing their weeks one week at a time, and from trading that they do with other exchange companies. Because of this, it's really hard to predict what will happen.
Do you have a deposit with strong trading power? Did you do a "request first," or a full deposit?