With global menu on the left part of panel :
With global menu at the center part of panel :
Is there is a kind of Z ( depth ) order for each part of panel,
left is at background,
right is just above left,
and center is at the top of both ?
Here are my top-panel settings :
( not the subject here, but you can also note there that screenshoting actual window takes a bit wider picture than actual window… )