Good job trying different things. It doesn’t make sense to me either, but based on past experiences that definitely means little. Did you feel any difference in how well the magnet holds for these different locations? The magnetic base couples with the metal to form the ground plane. It would be interesting to see if a non-ground plane antenna worked better in your specific circumstances.
Also, play around with your cable. You might have a problem that manifests itself when some portion of the cable is bent or straightened but not others. That could form an intermittent problem that coincidentally happens as you move the base around.
Radio is sometimes the most frustrating mystery, but I have found that most problems have simple solutions, propagation being the exception.