>_< someone should have read the WHOLE first post
those grey boxes are permanently there I designed my mod to only work in 1024x768 and 1280x800
however if you replace the xml files in the Main\Resources\Interface with the original files you can make it go back to being the original bland big grey area. In particular the building_setup_screen.xml it should revert/stay as the big bland grey huge box.
the smaller boxes were an experiment to see if I could get other pictures to load at certain pages and to see if I could make multiple grey boxes with the code. (turns out I couldn't just switch around and add values to make more boxes

)
if you just want to make the building management screen default replace the building_setup_sceen.xml
get the xml attachment I have on the first post that's the file you need.