Purpose’s of Tail Frames/Tail Box is for assisting the displaced air mass back to itself reducing power robbing turbulence.
If possible, the tail box should be positioned close to the rear/outside portion of the riders shoulders for best results.

Aero Wing tail frame forming a "tail box" on a Gold Rush
Many riders do not prefer the inconvenience of getting into a Body Socked bike – so - the tail box only concept is a great option.

Aero Wing tail frames are commonly used for Body Sock applications because of enhanced aero design and ventilation.
The same Aero Wing tail frame is used for Semi Streamlining this Gold Rush. A stretchy fabric “Lycra/Spandex” is used to cover the rider for aerodynamic streamlining. The tail frame simply finishes what the front fairing started. The shape and size of the Tail frame/box is important so to minimize turbulent drag.

Riders that have a "need for speed" usually end up using a lowracer inside a semi faired streamliner shape.
Note: – Keep in mind anytime cloth is used for streamlining, it is used for compromises of comfort and convenience. Smooth composite surfaces are known to be the fastest.

Hey Lonnie!
Great site! I could not agree with you more….Get rid of the “drag” and the speed is free! Personally, I am a 53 year old that has ridden for at least 48 of those years with knees to prove it.
Enjoy it while you can….
Jim
Thanks for the comment Jim – - your right about “Enjoy it while you can”.
So much is taken for granted “when you can”.