I can only imagine her when you mention that you were disappointed that the last box wasn’t as big as you expected. ;)
I had a vasectomy in Jan ‘03, and had only tried Magnum XL’s for the first time about a month before. I must have been about 5.6” girth and they fit fine.
Back when I purchased the Magnum XL’s is when I also blew them up to measure them, and they were 5.5” girth when blown up until they held their form, but not stretched. The Magnums I had were 5.25” girth similarly inflated.