I have a pair of the Shebeest BoardRider Capris and I noticed the same thing too... where the waistband is on the tighest setting but they still appear slightly loose and yet the biking shorts underneath fit just fine. I had ordered an XS so there was no smaller size to try. (I can also see what you mean about how going down a size would make them way more snug fitting.) I really liked the look of them, and since the chamois shorts and the length fit perfectly fine, I kept them.

Personally, I don't mind the looseness, as I use my board rider capris for mountain biking. I haven't noticed the fact that it's a little loose around the waist being an issue.All my other Shebeest apparel fits really well, so I'm wondering if it's a strategic decision to make the outer shell a little loose.