changing "place new tab (general rule)" to "panel start" in sidebery will put the new tab right at the top. unless you mean you want it only at the top of the g

changing "place new tab (general rule)" to "panel start" in sidebery will put the new tab right at the top. unless you mean you want it only at the top of the group? zen also has a "compact mode" than hides the native tabs, but it hides other things you might want as well