My firstmandolin was a round backed Martin. In those days it suited my anatomy a little better than it would today. A round backed mando and a round bellied musician don't work. I'm 6'1" , 230 lb and I can make my wife's 12 fret O-18 look like a ukulele.
A friend of my son, Manitoba Hal, is a great slide and blues musician who also likes to play the ukulele. The uke is a small instrument to begin with, but Hal is a very big man. Another case where musician and instrument look odd together.