you'll be overlapping layers on the inside of the kilt, as you ascend from fell to waistline.

The reason I didn't make the inner pleat edges actually meet (there's that fraction of an inch gap between the inner edges at the fell) was to minimize overlap at the waistline. If you really want deeper pleats, then you could make them that way, and live with the increased overlap at the waist.

When making a box-pleated tartan kilt, you'll likely make the maximum pleat depth at the fell, and then overlap a fair bit as you go up.