I much appreciate the long response. It was very helpful. I feel I have a much better understanding on svg, viewbox (you are right, the 100% is super invalid!!) and how to draw paths.
It seems that if i remove the aspect ratio of a path with rounded corners, they will distort, as they aren't being kept to scale. I am thinking (as design takes priority over animations) that I must settle with just drawing the rect and starting the animation from the corner.
Thanks for all of your help, this was very useful and taught me a lot!