How to figure out X,Y click offsets on circle of objects?

I have a ring of 32 images that is dragged radially (in a circle). Dragging is working fine, but I'm having trouble figuring out how to account for the initial X,Y click offsets, so the circle of objects doesn't jump when initially dragged. In the demo project (link below), when clicking toward the left side of an object and dragging, you can see the ring jump to match the mouse position. How can I determine the initial X,Y offsets to use to account for clicking anywhere on any image?

Demo: dropbox.com/s/29swpgn0wmbtuel/concentric_sample.c3p

Thanks in advance for any suggestions.

Rather than using an x and y offset, maybe you can try just saving the starting angle of your cursor from the origin/center of the circle, then using the anglediff expression to get the difference between the original angle and the current position and applying that to the position of your segments.