Exactly right.
I'm not sure there is any scope in terms of legality boxes to add bodywork in that area. It's outside the sidepod volume, which I think Mercedes used for their little downwashing vanes.
Williams provided some nice close-up shots of their car in their video on flow-vis.
They've added an optional air outlet in front of the rear suspension.
Flow-vis highlights a little outlet towards the end of the outer sidepod edge, presumably used for electronics cooling.