I’m not really sure what to call the neckband thingy, but I ended up finding Made by Rae’s tutorial that explained how to make the neckline I wanted.
This pattern is based off of Craftsy’s Sewing with Knits class. I made a striped knit t-shirt from this pattern a few years ago. The fabric is a Joann’s poly/cotton knit with minimal stretch, only 25-30%. The fabric is a little see-through, so I lined the front bodice with very thin jersey fabric I bought in the LA Fabric District. So glad it finally came in handy! I also used that fabric for the neckband, 85% of the length of the neckline circumference. The neckline is gapey. Next time I’ll try 80% length on the neckband.
I drafted a new neckline lower, for summer, and left a 1/4″ seam allowance. My neckband was 1″ wide and I topstitched 3/8″ from the edge. I think it fits well, and I’m pleased with it.