Avirex 1975 Wide Leg Jean Size 20 fits like size 8

Avirex sizing is different. They are labeled as size 20. I’m closer to a size 6 in jeans or a 28. These are slightly big in the waist for me. My measurements and typical sizes for reference (I am the one in the images). Bust: 37 in (34DD) Waist: 28 in Hips: 39 in Height: 5’ 7” My typical sizes Tops: S-M Jeans: 6/8, 28 Dresses: 6