The alpha channel itself shrinks about 1 to 2 pixels.
This is if you do any kind of cutting on the animation, if you don’t cut it at all its fine.
we had to retime some stuff and found it much quicker to just make the adjustment in final cut, but each time we did, the graphics would shrink just a little (1 to 2 pixels)
someone mentioned the animation codec can cause this in fcp 5.x