I was going to stay out of it because I am not a kilt maker, but this almost came up. There may be an additional steeking issue, though I'm not too sure about the first pleat having steeking issues. Supporting the pleat with stitching on both edges at the bottom of the fell does seem to help, and I experimented with this before I removed the fabric in the fell area on the Stillwater.

As stated the apron shape is an issue with some kilts, and a little reshaping might be needed.