I don't know how credible you are going to consider me, but my undergraduate degree is in costume. Not fashion, where you design for stick insects, but costuming where you have to make clothes that fit actual working humans who are going to sweat like mad eight shows a week.
"Natural waist" in costuming is the narrowest point around a human torso, starting below the ribs. If you take a piece of elastic, tie it snugly around you and go move around for a bit, where it rolls to on your body and stops is the natural waist.
Men's fashion has put the waistline for men's pants, below the natural waist since the 1960s. Beer guts have driven the pants-waist even lower.
Any human wearing low-rise jeans/pants is going to have their pants anywhere from 2"-4" below their natural waists to start.
I think this is where the strategic word "sagging" comes in. Make sure your lowriders are skinny jeans from now on, peeps!