I had (thought I had) the same problem with my SC. I have the same set up as yours, only I have a TP 1320 LiPo. Being new to 3D I wanted to balance the plane to specs. With the the battery hanging of the nose, and 1.5 oz. lead on the other side It balanced at the 3" mark. I was very disappointed with the plane at that point as well. It was weighing it at 20 oz with the lead on it.

So upon the test flight I set out to set up the CG. After the first flight the lead came off, from there the battery went further, and further rearward. The CG is now 4 to 4 1/4" back.

I now have 54 flights on her without missing a beat! All I do this plane is flyit! I can't say enough good about this plane!

I am now doing maneuvers I though were never possible