The wheel was set up correctly--I had it the slowest (largest) whorl on the Matchless. The problem--I treadle too fast which lent itself to making a thinner yarn. I had to force myself to pay attention and spin slowly and make sure I was getting enough fiber into the yarn.
When I started this project, I was simultaneously spinning a very fine yarn on another wheel, so perhaps I thought what I was spinning was thick enough. This mistake, and waste of roving, has me thinking I might be better off concentrating on just one spinning project at a time.