A couple of other elements in this that got me thinking/analysing.. (sorry for my free flow writing style, my thoughts on this are under development..)
The head and feet stretching part:
Relating to Alice in Wonderland Syndrome (macropsia or Micropsia), the feeling of body spatial distortion on the verge of sleep (related to sleep paralysis)..
This phase of sleep onset tends to be where most people lose consciousness, so the idea of incorporating body distortion into the visualisation process, potentially could retrain the brain to be conscious for this part of the process.
This idea is a reflection of other common WILD techniques, e.g. Monroe's technique of imagining how nice it would be to fly/float..
It also could be stimulating that part of the (right?) Temporal lobe that is associated with spacial awareness, and of the perception of self within physical space.
Perhaps also related to that sense of falling as you are dropping off to sleep?
The front door visualisation:
Engaging memory, maybe a hippocampal stimulus (the hippocampus has been associated with out of body perception) also creating introspection and drawing attention away from the outer world is an important step towards dreaming..
Flying over house, engaging imagination and attention to detail. Movement visualisation creating REM. Also changing the lighting effect (night to day to night) helps establish control over environment (hmm, is this necessary)
My interest in this technique is also partly due to my aim to create an effective lucid dream hypnosis recording, this is why I am breaking it down thoroughly.