Bullets work off of the objects angle. It just so happens that the angle for 0 is east, or that way->.
So if you want the bullet to travel down you would set its angle to anything below 179, and above 0, up, above 180, etc.
Image points have very little to do with it. However the hotspot has quite a bit to do with it, as it is the objects origin, or the xy that the system will use.