Lens Depth Distortions

 Wide Angle                                    

18mm

- Camera approx. 1 meter away

- Lockers distorted and stretched

- Subjects' body are distorted and stretched

- Subjects seem bigger than the lockers

 Telephoto

55mm

- Camera approx. 3 meters away

- Distortion eliminated from the subjects and lockers

- The picture became completely flat

- The subjects have become smaller than the lockers

 Wide Angle

18mm

- Camera approx. 1 meter away

- The subject and table are distorted and stretched

- We see a lot of insignificant/irrelevant information in the background

 Telephoto

55mm

- Camera approx. 3 meters away

- The subject and table became flat

- No insignificant information in the background

 The Take Away ( i.e. what you learned from this)
          - what happens to the width of the background when you go from WA to tele?

When we go from WA to tele, the width of the background becomes more tight. We don't see as much information or details than WA.

          - what happens to the distance between the background  & subject "  "  "  " "  "  "?

It makes it as if the subject is close to the wall than WA, everything seems to be far away and distorted. 

          - what happens to the subjects themselves in terms of expansion & contraction (for
            the width) as well as compaction and enlargement (for front to back)?

Everything becomes flat. The distortion and stretching is eliminated.

  Scenario: imagine that you're shooting a model (full body) against a seamless. Your
  framing of the model is what you want but the edges (and beyond) of the seamless are
  visible in your frame. You don't want to move the model back towards the seamless and  
  you don't want to have to retouch out the seamless edges. Applying what you learned
  from this exercise today, what's the solution using just your camera & lens?

I'd put to telephoto (55mm if lens with 15-55mm), and I'd back off until the model fills in the frame of my camera.