In an AR world the only limits are the screen borders. We need to suggest to the user the most natural possible movement.
Da Vinci’s Vitruvian Man makes a reference for the human’s upper limbs that we may translate into an elliptical natural movement
The blinking of the chair icon gives a sense of "missing chair" which is crucial to understand the task immediatelly
A centered UI makes the job, but I think it might feel like a "weird compass"
The UI located on the edges helps understanding intuitively that the screen edge is the limit, providing a more natural feel.
Rafael Parra-Toro