This led me on to something and I was playing with value curves in the render buffer.
It seems like when you apply a render buffer to just one of the four points, top left bottom or right, it opposite is also effected, OR xlights moves the whole buffer and everything inside it to the value in the curve. (see attached xpreset bouncing ball), is that what it supposed to do?
Because, if you then apply a value curve to the oppsite side the effet in the buffer "wobbles" (see attached xpreset bouncing ball 2)
Is there away to move the points and have the opsite point not move? Essintaly I would like the ball to stay still but the buffer to move, and if you change the circile to across and the top bottom value you cuves to left right you may see why....

Hope I explained this right.....