I was just playing with the warp effect and having a lot of fun but I did notice that the centering with the X & Y doesn't work as expected.
When I applied the warp effect over a picture on a 128 by 128 Matrix I have to set the x at 51 and the Y at 49 to get the effect to Center on The Matrix.
When it set at 50 and 50 the effect is in the lower left corner of The Matrix.
But then again maybe I'm not applying it correctly.