Reflex~ Ivory~ Size L 10/12 fits more like a 8/10

I bought this from a clothing boutique about a month ago. Brand new and only worn once to try on when I got it. Super soft Sherpa zip up (Ivory). Hood and side pockets and the sleeves and the bottom hem is a stretchy ribbed knit cuffs. The inner liner is a nylon mesh material. Relaxed fit. It’s a large 10/12 but fits more like a 8/10.