-DSHOW_POSITION could show the entire window dimensions (including window decorations)

I'm struggling with this option.

Check the attached image, a screenshot of Mozilla Thunderbird.

XFWM4 shows: 1505x805. The screenshot comes off as 1600x900. A difference of random 95 pixels in both dimensions.

Would be great if there were a compile time or XFCE option to show the entire window dimensions vs. what's shown right now.

Thank you very much!