@Simone I updated the documentation a while ago to include the second method, and it was then pointed out that the skew calculation output the skew factor with the incorrect sign. See https://forum.duet3d.com/post/307701
I was going to check it and update the documentation, but I forgot! But as @CalinFlorin86 pointed out, if the angle was acute (ie AC > BD) the skew factor should be negative, and if the angle was obtuse (ie AC < BD) the skew factor should be positive. I have updated the documentation to note this, and updated the macro so the output should be correct.
That the numbers you are seeing are basically the same (XY: -0.00146 the first time, and Skew factor: 0.0014215 the second time, though this should be negative), it sounds like skew compensation was not active the second time. Otherwise the print would be square, I think.
Ian