Depth perception is a product of many senses contributing data that your mind processes. Relative size, color brilliance, dead reckoning, sound and probably others. The most reliable one for me is dead reckoning. Sailors and pilots use the term to describe the process of deducing where they are based on where they were adjusted by the progress (time, speed and course). We RC fliers probably aren't even aware that we use it to assist with our depth perception. I know for sure that I do and think it is likely that others do as well.

For example... we have tall trees at the North end of our field where a good many fliers have roosted.... my self included although mine wasn't because of a too long landing pattern as most are. My procedure to acquire depth perception about the landing pattern is to time how long I fly the down wind leg after the plane crosses in front of me. I rely far more on that time and speed element than I do my eyes.

Many times there are just too many planes in the air to use noise as a reliable input. Eyes alone are inadequate and unreliable. Some may claim otherwise but I think they would be fooling themselves. Relative size is a good one, but not as reliable for those of us who fly varying size planes.