If this is as simple as FOC I will be terribly embarassed. Doegirl said the same thing above. Why was I thinking that FOC wouldn't alter the flight that quickly, in 20 yards I mean. (pool cue theory)
Is it really that simple?

Spine refers to the stiffness of the shaft. It affects the way the shaft flexes in its flight. If you make the arrow front heavy the arrow will flex more and keep flexing or oscillate too much during its flight. A underspined arrow (too flexible for the application) will cause the arrow to impact the target with its tail to the left. So the anwer about foc and spine are affectively the same. A crazy foc like the having the balance point towards the rear will cause erratic maybe dangerous flight but a small change in foc should cause a change in impact.
Try one or a couple of arrows of a different spine or a different weighted point to see what happens. You can go to a 160 grain tip which will make the arrow flex more to see if that goes left or right of the point of impact. This will affectively change your spine as would the length of the arrow.
I hope this isn't too confusing.
Easton's tuning guide will bring some enlightenment to the subject.

Check this out David.
http://s28.photobucket.com/albums/c220/autotrend/?action=view&current=compound_bow.flv

Thanks Don, that makes good sense.. Here some more of the story, fits your description perfectly..
If you look at the two pictures I posted you will see the second one has the tape lower than the first, this is because in my initial shooting I had a pass through with my first arrow, it hit above the targets padding and stuck into my shop door. When I did manage to pull the arrow out it left the tip and insert deep in the wood. I went inside and put in a brass insert and tried again, it missed the target by about two feet and stuck in the broad head target you see in the photo, I noticed it was bent pretty bad when I pulled it out, couldn't figure out why, now I know.
I am putting these on the back burner until I figure out my scope..