Part of it, I'm guessing, is the depth of field. The janitor bot is in sharp focus, but the little bot in the background, which looks like it's very near the janitor, is very out of focus -- as are the foreground rocks. This makes it look like a very narrow depth of field, which is the effect you see when you take a picture of a small model from very close to it.
Try widening up your DoF so that the background spaceship is only slightly blurry, and see if that makes a difference.
You could also try moving the camera about halfway down towards the ground, so the janitor looms, and perhaps scaling the distant little bot down a bit so it looks as far away as it is (the narrow viewing angle disguises the distance quite a bit; the closer you zoom, the less an object's apparent size changes with distance).