Unity and VR: offset using "ReadPixels()" function - unity3d

Question

I've ran into a small issue developing a picture taker for a VR project. I need to take a screenshot of a specific zone, which is a rectangle with variable width and height. To do that, I have a transform anchored to the top right corner of the bounding box that represents where the picture is going to be taken, and one anchored to the lower right corner.
Here's what it should look like. I've added little red circles to show the transforms's position.
Here's what a screencap using the left eye looks like. It's the same result if I use "both eyes" as a target in the Camera settings.
Here's what a screencap using the right eye looks like. So not only is it too far left or right, it's also a tad too high.
Here's the code that creates the Rect, and here's the code that reads the pixels.
When the Main Camera targets the left eye, there's almost half of the Rect's with as an offset to the left, when it targets the right eye, there's that same offset to the right, when it targets both, there's a softer offset to the left, and all of these have a slight vertical offset upwards.
Any help is appreciated. I'll keep this thread updated if I find anything!
public void SubmitPicture()
{
Vector2 upperLeftPosition = mainCamera.WorldToScreenPoint(upperLeftTransform.position);
Vector2 lowerRightPosition = mainCamera.WorldToScreenPoint(lowerRightTransform.position);
pictureBoxRect.x = upperLeftPosition.x;
pictureBoxRect.y = mainCamera.scaledPixelHeight - upperLeftPosition.y;
pictureBoxRect.width = lowerRightPosition.x - upperLeftPosition.x;
pictureBoxRect.height = lowerRightPosition.y - upperLeftPosition.y;
pictureSnapper.OnInput(AbsoluteRect(pictureBoxRect));
}
public void OnInput(Rect pictureBox)
{
if ((int)pictureBox.width > 0 && (int)pictureBox.height > 0)
{
videoPlayer.Stop();
Texture2D videoTexture = new Texture2D((int)pictureBox.width, (int)pictureBox.height);
videoTexture.ReadPixels(pictureBox, 0, 0);
videoTexture.Apply();
byte[] imageData = videoTexture.GetRawTextureData();
if (debug)
{
byte[] imagePng = videoTexture.EncodeToPNG();
File.WriteAllBytes(Application.dataPath + "/" + savename + ".png", imagePng);
}
}
}
private Rect AbsoluteRect(Rect rect)
{
if (rect.width < 0)
{
rect.x -= rect.width;
rect.width = Mathf.Abs(rect.width);
}
if (rect.height < 0)
{
rect.y += rect.height / 2;
rect.height = Mathf.Abs(rect.height);
}
return rect;
}
Updated to add the picture references.