Visibility, placement and roles of system bars can be controlled using RRO in config.xml
<bool name="config_enableTopSystemBar">true</bool>
<integer name="config_topSystemBarType">0</integer>
<integer name="config_topSystemBarZOrder">1</integer>
I would like to as well control wether the bar is always on or if it shows only with a swipe.
I haven't been able to find a config in SystemUI or Car/SystemUI. This can be changed from the command line (but forgot how)