Yar- I messed with a four panel design (two curves at the hips and a flat panel at front and back), end result- put enough segments in and you have a cone anyway. The fabric figures it out. You want it loose for airflow anyway, keep the form fitting one for trail town bar visits.
For a skirt- measure your waist at the top of your hip belt, not your true waist. I haven't yet solved the "women's" problem in that regard, and my wife has complained a hair about the bunch up of fabric using a drawcord because of the hip to waist differential in women. The complaint is an aesthetic one though, nothing else. If they have one, a fellas ass sticks out but hips are generally straight so it doesn't show up as much as it does in the ladies versions.
Lost the link, but there was a thru-hiker gal who made hiking skirts with a "yoga" pant style top to solve the issue. The top 4-6" were made of a stretch lycra. In a rain skirt though- poor choice.
FWIW- I gave up on the rain skirt for the most part. I've found just an uncoated nylon to be the best all around. Dries in 15 minutes, and I tend to sweat enough in the rain skirt to pretty well defeat the purpose. Around 55 degrees I occasionally wear a coated (rain) version for a little more warmth. When it's below 35 or so, I'm more likely to slip pants on anyway. So the rain skirt never really found a spot in my kit personally.

