Dear Nick
Looking at the image it looks to me as if the wheelchair is pushed in from the rear and the vehicle is wide enough for two wheel chairs or a wheel chair nand a seat, hence the rear wheel in the centre and the high sides. I am sure that there must be a floor lowering mechanism as well by the looks of the angled bars between the floor and the side skirts.
It all looks a little Heaf Wobbinson, but interesting.
Chris Thomas