The sizes look ok to me. Only the sand texture... but this is something you know already i am sure. Perspective. You are right, the further away onjects are the smaller they look. My experience is to trust 3D programs. They do perspective looks very well and very correct. IF WE LET THEM DO IT. So my advice always is to size the objects relative to each other correctly. Then you will always be correct and not in trouble when you move the camera in the scene to find the best pov for a specific setting.

One day your ship comes in - but you're at the airport.