Smart thinking there, batman. I've never thought of 'extending' the backplate photo downwards like that. I tend to just use an invisible shadow catcher plane under the model, but that limits the choice of backplates a bit. Many don't include enough close-in foreground for figure shots, they work for car shots which are further away, but if as you bring a figure closer in the feet will often go out of frame. This opens up a bunch of possibilities, assuming one can always fake the ground surface as successfully as you have done here.