Careful, downwash doesn't produce lift, downwash is produced by lift. Depending where downwash is produced the effect and severity will be different (e.g. in ground effect downwash is reduced even though lift will be increased).
The fins on the sidepod will be helping flow to cling to the sidepod surface, especially where they sweep downwards agressively - this helps drag and "feeds" air to the diffuser as well as helping the rear wing. Lift/downwash created under the drivers legs helps to draw "clean" air down into the sidepod undercut, and prevents the front suspension wake going into the cooling ducts - it also helps increase the effective angle of the floor, producing more downforce.
A small amount of lift can produce a bigger amount of downforce.