If your coverstitch machine has 3 needle positions, try using a narrow hem on soft knits. I was in the habit of always using the widest hem option on my coverstitch machine, but I have seen the light!
See the “tunneling” in the middle of the hem in the image above?
Ahhhh, that’s better! I just figured this out!
Give it a try. I think there are way fewer issues with hems “tunneling” when using a left + center needle position rather than the wider left + right needle position while coverstitching. Let me know what you think!