[aerohead]

On the dragsters,the pseudo-Jaray tail will be dominated by a large wake of low base pressure and strong longitudinal attached vortices which will create lift.
The spoiler will give the air a place to re-attach to before saying adios to the bug,negating the lift.The capping plates help prevent transverse air-bleed around the outer edges of the spoiler,increasing its effectiveness,and also provide a little weather vane surface should the car get crossed-up on the track.
The wash coming off the spoiler area will be better for parachute(s) deployment.