Ok, so guess-and-check it is! I had a feeling that would be the answer but figured it was worth asking!
I've played with the tension already - that was my first assumption but I could only make things worse but not better. I gave up on that in frustration (I usually am pretty good at fixing tension so I was annoyed it wasn't working) and had an "ah-hah" moment just yesterday that it's probably the presser foot pressure causing me fits. And then that led me to thinking about the bobbin tension test and wondering if there was something similar for presser foot pressure.
