When two objects having the same sizes are drawn in perspective, the one in front appears a little bigger than the one at the back in order to show depth of visual perception. I drew the stationary train in front of the platform, so naturally the train should appear a little larger than the slightly smaller platform behind it. A drawing of a flat surface made seen from the top, just like what you did, cannot show depth properly. Drawings are just visual representations and they do not determine the values of the quantities that must be used in the computations.