If you are using radios both parties need to practice, especially if you are not accustomed to them. People speaking before the radio even keys up is a common issue. Sometimes the word STOP is spoken before the radios have a chance to even connect.
Radios are a good tool, but if you are using a back up person and you can't see that person in the mirror then your foot needs to stay on the brake.
My job requires that whenever backing we have a backup person. We all have our ways but my procedure is the passenger gets out and goes to the left rear side of the rig, near the corner. I want my backup person to move where he/she want the rear of the rig and when that person goes out of sight in the mirrors I don't move until they walk back into view.
Just about a year ago I went to the funeral for an Elizabeth, NJ veteran firefighter close to retirement. The engine pulled up on a working fire, the FF got out to back his driver into position, the backer slipped on the ice, the driver didn't see him and ran over the FF, killing him instantly. One FF lost and another's life ruined.
Be careful.
Make it clear to your spouse that you will not move if you can't see him/her.