Jan - adjusted planet's radius, air and dust (haze) depth and size of the landscape. Avoided vertical exaggeration. This whole thing is just a "I wonder what it looks like in real life, so maybe I'll render it to see," and trying to match the Rover pictures as closely as I can regarding colors, surface textures, sky, etc.
Yes, it's really, really hard to get any sense of scale in these views. No trees, buildings, people, etc....so the rocks might be an inch across or 100 feet across. No way to tell. Only sense of distance is the haze. Rocks I used are actually 10 to 30 meters across (3 fake stone populations), which might be bigger than they really are on Mars.
Sky color - wonder how much the dust in the sir in Mars varies from year to year, and if the sky's hazier during dust storms. Thought about trying to have dust clouds, but don't see them in the Rover pix. Learned while setting up these scenes that the color of the haze (dust) has a huge effect on sky color. Make the "dust" more chromatic, or redder, or yellower, and it changes the whole look of the sky.
By the way, I really like your pictures of a terraformed Mars!
