Are you saying that things look different when looking in the mirror, if the end of your trailer is 48 feet away?Just for the record, backing up to an empty dock in an empty parking lot isn't the easiest thing to do. Especially if there are no lines on the pavement. Nothing to judge distance by!
I use the backup camera in Wife's car simply to make sure there is nothing directly behind the car before I start moving, but otherwise use side mirrors.
The hardest trailer to back up is a cement mixer! The shorter the trailer, the harder it is to backup! The big ones just take more real estate, which has its own issues!
I used to drive a C-65 with a 20'(?) rack body, with a hay mulcher on back. Trying to back that up was a challenge, to say the least. The body was 8 feet wide, usually loaded with hay; the mulcher was about 8 feet long and 5 1/2 feet wide. By the time that it showed up in the mirrors it would be jackknifed... and the forewoman on back would be screaming at me.
Actually she only did that once... scream at me and I scream right back.