could it be that the transformation you receive is supposed to convert from marker frame to camera frame?
then a positive Y would mean the marker is moving into the bottom half of the camera’s frame/view.
point the camera directly at the marker’s origin, but angle the camera so it’s not above the origin. what values do you get?
the screen coordinate system in OpenCV is usually right-handed and x right, y down, z away. I don’t know if aruco does anything differently.
it would be immensely helpful if you showed some pictures that show where the marker is and where your camera is, and what values you get for that pose… and the same for another pose.