skew image with matrix, top angle good, bottom flat

Hello:

I am trying to skew an spark Image object using a matrix. The problem I am having is that it only effects the top angle. I think it may be related to the position of the image (x and y). The top angle is prefect but the bottom is flat!

Here is a bit of code:

//imgA = pixles down from top left coord, I used arctan with oposite over adjacent to get a radian angle

//size

openImage.width = imgW; //say 200

openImage.height = imgH; //say like 300

//angle & poisition

var ooa:Number = (imgA / imgW); //perhaps 20 / 200

var angle:Number = Math.atan(ooa);

var m:Matrix = new Matrix();

m.tx = imgX; //over 400

m.ty = imgY; //down 500

m.b = angle;

openImage.transform.matrix = m;