Leggings need to be really comfy and very stretchy both at the hem and waistline. They are cut to fit and as they are being pulled over the waist those coverstitches may need to stretch 25% or more. Here is an example of settings for cotton lycra with regular polyester overlocking thread on cones. I sew the hem with the leg turned inside out and stretching gently while sewing to work as much thread as possible into every cm/inch.

SETTINGS for the Babylock CoverStitch:

Stitch length 2.5

Differential 1

Needle 1 tension 2.5

Needle 3 tension 4

Looper tension 1.5

The waistband especially needs to be extra stretchy. The stitches are really close together but still neatly interlocking. Please notice how setting the tension for needle 1 on 2.5 is necessary when there is only one layer. If I would use a higher tension here, this would result in tunneling.